Axial member with flange, connection member and production methods thereof

ABSTRACT

A target tubular member with flange, such as a bumper stay, has a flange having an outer diameter larger than the diameter of an axial section and is formed by electromagnetic forming without excessive expansion. The tubular member with flange includes an axial member made of a tubular aluminum alloy extrudate and a flange member joined to an end of the axial member. The axial member has an end flange being integrated at its end and having an area smaller than that of the flange member. The flange member has a hole, and a cylindrical hole flange at the edge of the hole. The axial member fits in the hole of the flange member, the end flange is in intimate contact with the flange member, and the outer periphery of a small-diameter portion of the axial member is in intimate contact with the inner periphery of the hole flange. The hole flange is held between the end flange and a protrusion. The tubular member with flange may be produced by inserting an untreated pipe into the hole of the flange member and expanding the untreated pipe by electromagnetic forming.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to axial members with flange having anaxial section made of an aluminum alloy material and a mounting flangearranged at the end of the axial section, to connection members and toproduction methods of these members.

2. Description of the Related Art

Bumpers arranged at the front end (front) and the rear end (rear) ofbodies of automobiles such as passenger cars and trucks have bumperreinforcements as reinforcing members inside thereof. Such a bumperreinforcement is generally a member which is hollow in cross section andincludes a front wall and a rear wall pointing substantiallyperpendicular to a loading direction, and a horizontal wall connectingthese walls. The bumper reinforcement is supported by a pair of bumperstays from the rear, and the respective bumper stays are fixed at theirrear end to the front end of the side member (front or rear).

Aluminum bumper stays are roughly classified as bumper stays to bevertically crushed, and those to be horizontally crushed. With referenceto FIG. 79( a), such a bumper stay to be vertically crushed includes anaxial section 1 and sheet mounting flanges 2 and 3. The sheet mountingflanges 2 and 3 serve to mount a bumper reinforcement 4 and a sidemember 5 and are weld to the front and rear ends of a hollow extrudateconstituting the axial section 1. This type of bumper stay has anextrusion axial direction pointing to a cross direction of a car body ina direction substantially perpendicular to the longitudinal direction ofthe bumper reinforcement 4. With reference to FIG. 79( b), a bumper stayto be horizontally crushed includes an extrudate 6 and has an extrusionaxial direction pointing to the vertical direction of a car body in adirection perpendicular to the longitudinal direction of the bumperreinforcement 4. The extrudate 6 integrally has mounting flanges 7 and 8at the front and rear ends thereof. Examples of bumper stays to behorizontally crushed can be seen typically in Japanese PatentApplication Laid-Open (JP-A) No. 08-91154, JP-A No. 2000-318552 and JP-ANo. 2001-294106.

Bumper stays to be vertically crushed generally have a high productioncost, since the constitutional three parts are integrated by welding. Inaddition, if a mounting section at the end of such bumper stays isinclined rearward with respect to a width direction of a car as shown inFIG. 79( a), the axial extrudate must be cut obliquely. This invites adecreased yield, an increased cutting cost and an increased weldingcost. Bumper stays to be horizontally crushed are low in theirproduction cost and can be easily produced even if the mounting sectionat the end of the bumper reinforcement is inclined or curved withrespect to a width direction of a car. However, these bumper stays havea lower energy absorption per unit weight and lower effects in weightreduction than the bumper stays to be vertically crushed.

Japanese Patent Application Laid-Open (JP-A) No. 2004-42066 describes atechnique for forming mounting flanges 12 and 13 at both ends of anaxial section 11 by electromagnetic forming, which axial section 11 ismade of an aluminum alloy extrudate (tube), as shown in FIG. 79( c).

This article is produced in the following manner as shown in FIG. 80.Initially, an aluminum extrudate is cut to a predetermined length toform an untreated pipe 14, a mould 15 including plural mould parts isallowed to surround the untreated pipe 14 while the ends of theuntreated pipe 14 are protruded from end faces (molding faces) 16 and 17of the mould 15. An electromagnetic forming coil 18 is inserted into theuntreated pipe 14, and an electric energy (charge) accumulated at a highvoltage in the coil is instantaneously discharged to thereby produce thearticle. In the electromagnetic forming process, the electromagneticforming coil 18 generates a strong magnetic field in a very short timeas a result of application of electric energy, a work (article to beprocessed) placed in the magnetic field receives strong expansive forceand/or contractive force by the action of a repulsive force of themagnetic field (the Lorentz force in accordance with the Fleming'sleft-hand rule) and is plastically deformed at high speed to therebymold the work to a predetermined shape. In the illustrated example, theuntreated pipe 14 in a region inside the end faces 16 and 17 expandsoutward in a radial direction by the action of the strong expansiveforce, is pressed to the inner face of a through hole 19. The untreatedpipe 14 in a region outside the end faces 16 and 17 spreads and strikesagainst the end faces 16 and 17.

The electromagnetic forming can be applied even to the case where thework must be processed into a complicated shape, since the work isdeformed at high speed. In addition, this technique enables a shape withgood precision, since the work is pressed to the molding face of themould to form a predetermined shape. Accordingly, flanges having variousshapes corresponding to the shapes of the mounting faces can be obtainedby allowing end faces (molding faces) 16 and 17 of the mould 15 to haveappropriate corresponding shapes. Examples of possible flanges are aflange having a plane perpendicular to the axial direction (flange 13),as well as a flange having a plane oblique to the vertical plane to theaxial direction (flange 12), and a flange having a curved face.

The electromagnetic forming itself has been known, as describedtypically in JP-A No. 58-4601, JP-A No. 06-312226, JP-A No. 07-116751,JP-A No. 2002-86228, and Search Report of Mechanical EngineeringLaboratory, No. 150, “Plastic Working Using Magnetoelectric Force”(March 1990, published by the Mechanical Engineering Laboratory, MITI,Japan)

In the conventional bumper stays to be vertically crushed, the threeconstitutional parts are weld at an intersection of the axial sectionand the flanges at which a load upon collision is most applied. Thus,they exhibit decreased properties of the materials, which may inviteunexpectable decrease in energy absorption, in addition to theabove-mentioned disadvantages.

This problem is solved by allowing both ends of a tubular aluminum alloyextrudate to expand typically by electromagnetic forming and therebyforming flanges integrally with the axial section. In this case,however, deformation of the flanges due to tensile force to acircumferential direction increases with approaching to the outside,which invites reduction in thickness and, in turn, invites cracking.This problem becomes more serious when the flanges have larger diametersas compared with the diameter of the axial section made of an aluminumalloy extrudate.

The cracking problem is specifically serious in the case of an aluminumalloy extrudate having a fiber structure. Such a fiber structure mainlyincludes grain boundaries in parallel with the extrusion direction, andmolding force for expansion applied typically by electromagnetic formingacts in such a direction to break or tear the grain boundaries. Inaddition, an article having a fiber structure less elongates in adirection perpendicular to the extrusion direction. As is well known, analuminum alloy extrudate having a fiber structure exhibits excellentcrush properties in an axial direction and is highly useful as a bumperstay. However, such an aluminum alloy extrudate exhibits lowermoldability in an expansion direction than an article including anequiaxial crystal, invites cracking specifically in the case whereflanges are formed at ends thereof and thereby the flanges cannotsignificantly have sufficient sizes to be connected with a bumperreinforcement and a side member.

FIG. 81 illustrates the state where a flange 12 (and also a flange 13)formed by electromagnetic forming has a decreasing thickness toward theoutside. As is illustrated in FIG. 81, the flange 12 has a varyingthickness in a radial direction and a front 12 a of the flange 12 is notflat even if an end face (molding face) 16 of a mould 15 is a flatplane. When the resulting flange 12 is fixed, for example, to a rearwall 4 a of a bumper reinforcement 4, there is a gap G between theflange 12 and the rear wall 4 a of the bumper reinforcement 4, asillustrated in FIG. 82. The gap G invites distortion of the flange 12upon fixation with bolt and nut or by riveting, and invites a spacebetween the fixed flange 12 and the rear wall 4 a of the bumperreinforcement 7. This is also true for the case where the flange 13 isfixed to the tip of a side member. This problem becomes more seriouswhen the flanges have larger outer diameters as compared with thediameter of the axial section made of an aluminum alloy extrudate.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of thesedisadvantages of conventional techniques, and an object of the presentinvention is to provide a tubular member with flange that has an axialsection free from welding spots, has a flange having an outer diameterlarger than the diameter of the axial section without excessiveexpansion and is usable typically as a bumper stay.

U.S. Pat. No. 6,255,631 discloses a technique for joining a cross memberand a channel side-rail of automobile by electromagnetic expansion (FIG.83). The channel side-rail 19 and the cross member 20 however may becomeloose when, for example, an intensive rotative force is applied on thechannel side-rail 19, since they have no engaging part around the axis.If the channel side-rail 19 and the cross member 20 become loose orrotate relatively, the inner periphery of a through hole of the channelside-rail 19 slides with respect to the cross member 20, and at leastone of the two members is worn at the contact portion, which furtherincreases the looseness.

Thus, looseness of a structure, such as a channel side-rail with a crossmember or a bumper reinforcement with a bumper stay, invitesdeterioration in rigidity of the structure and causes vibration.

Accordingly, a second object of the present invention is to preventrelative rotation between an axial member and a flange member around theaxis of the axial member, which axial member has been formed byelectromagnetic expansion and which flange member has a mounting face tobe in contact with a mating face of another member.

When an axial member instantaneously spreads and comes into intimatecontact with a flange member, the axial member intensively hits againsta flange face around a hole. The hit portion bends and deforms by theaction of the striking force. In this case, the flange member may bejoined to the axial member while the hit portion is deformed. Inaddition, when the flange member is mounted to a mating face of acounter member, a load applied by the counter member on the flangemember may cause distortion. This problem becomes serious specificallywhen the mounting face has different levels.

Thus, a third object of the present invention is to carry out joining ofa flange member while preventing deformation thereof.

A fourth object of the present invention is to prevent a flared portionarranged on a tip of an axial member from obstructing the mounting ofthe flange to another member in the case where the flange to be incontact with a mating section of another member such as a bumperreinforcement or a side member is fixed to one or two ends of the axialmember by electromagnetic forming.

A certain bumper stay includes a hollow main body of a bumper stay to behorizontally crushed as illustrated in FIG. 79( b) and a hollow axialmember arranged inside the hollow main body. In this bumper stay, theaxial member is positioned typically by deforming and crimping a pair ofridges integrally formed inside the hollow main body or by screwing ascrew or pin into a hollow portion of the axial member from outside thefront and rear walls. The resulting bumper stay has an extra increase inweight, and the axial member is positioned with insufficientreliability.

Accordingly, a fifth object of the present invention is to reliably fixa bumper stay main body to be horizontally crushed to a tubular axialmember for reinforcement without extra increase in weight and to preventthe axial member typically from misregistration.

Specifically, the present invention provides a tubular axial member withflange, including:

-   a flange member having a mounting face to be in contact with a    mating face of another member; and an axial member being made of a    tubular aluminum alloy material and having an end joined to the    flange member, wherein the flange member has a hole, and the axial    member is placed in the hole, wherein the axial member has a flared    portion at an end thereof, the flared portion spreading in a radial    direction as a result of electromagnetic forming and being in    intimate contact with the flange member, and wherein the axial    member has a protrusion formed by electromagnetic forming, and the    flange member on the periphery of the hole is held between the    flared portion and the protrusion.

The above configuration according to the present invention enables anaxial member with flange, such as a bumper stay, which has an axialsection free from welding spots and has a flange having an outerdiameter larger than the diameter of the axial section without excessiveexpansion. In addition, such a tubular member with flange can beproduced by joining an axial member and a flange member by means of akind of crimping by one procedure of electromagnetic forming withoutusing welding or mechanical joining according to necessity. Thetechnique does not require excessive or forced expansion and can use analuminum alloy extrudate having a fiber structure as the axial member.When the resulting article is used typically as a bumper stay, itexhibits excellent properties upon crush.

The tubular aluminum alloy material can be an extrudate as well as atubular molded article formed by winding a sheet material.

In the axial member with flange, the outer periphery of the axial memberis preferably in intimate contact with the inside of a hole flange ofthe flange member. This stabilizes the flange member joined to the axialmember and enables easy positioning of the two members duringproduction.

The present invention is applicable not only to bumper stays but also togeneral connection members (connection structures).

In the axial member with flange having the above configuration, it ispreferred that the hole is arranged to the rear of the mounting face ofthe flange member, and the tip of the axial member is flush with or tothe rear of the mounting face of the flange member.

It is also preferred that the hole is a burring hole being burred fromthe front, the axial member has an end spreading outward in a radialdirection and in intimate contact with the inner periphery of theburring hole, and the tip of the axial member does not protrudefrontward from the burring hole and is flush with or to the rear of themounting face of the flange member.

This prevents a flared portion formed on the tip of an axial member fromobstructing the mounting of the flange member to another member in thecase where the flange to be in contact with a mating section of anothermember is fixed to one or two ends of the axial member byelectromagnetic forming.

In the axial member with flange having the above configuration, theflange member can have a device for preventing the axial member fromrotating. This prevents relative rotation between the flange member andthe axial member after electromagnetic forming, since they engage witheach other by forming the front or rear of the flange member or theinner periphery of the hole to a specific shape.

The “axis” of the axial member herein means a straight line being inparallel with a longitudinal direction of the axial member and passingthrough the center of the hole.

In the present invention, when viewed from a hole of a sheet member, theside toward the flared portion (axial flange) is defined as “front(forward)”, and an opposite side is defined as “rear (backward)”. So, aplane facing forward is defined as “front face (front)” and a planefacing backward is defined as “rear face (rear)”.

The flange member can be non-axisymmetric with respect to the axis ofthe axial member on the front or on the rear thereof. This configurationis typically applied to a region of the flange member around the holewith which the axial flange is in contact. The configuration means thatthe front face of the flange member has a geometric shape varying aroundthe axis. The use of the flange member having such a shape makes theaxial flange and the flange member after electromagnetic forming engagewith each other and thereby prevents relative rotation between theflange member and the axial member. In contrast, if the front or rear offlange member in the region is axisymmetric with respect to the axis ofthe axial member, the axial flange and the flange member do not engagewith each other at any point, and relative rotation between them is notprevented upon application of an intensive rotative force.

In the axial member with flange having the above configuration, aportion of the flange member against which a protrusion of the axialmember formed as a result of electromagnetic forming hits, namely, aregion of the flange member around the hole may be thickened. Thisconfiguration prevents distortion and deformation of the portion duringelectromagnetic forming and avoids the necessity of a mould to be incontact with the flange member for backup during electromagneticforming. In addition, the configuration more effectively contributes toweight reduction than the case where the entire flange is thickened.

In the axial member with flange having the above configuration, it ispossible that the flange member is made of an aluminum alloy extrudate,the flange member comprises an outer portion, an inner portion, and ariser or ramp, the outer portion has a step height with respect to theinner portion, and the riser or ramp connects the outer portion and theinner portion, the outer portion is located to the front of the innerportion, the front face of the outer portion serves as amounting face tobe in contact with a mating face of a counter member, the inner portionhas a ridge on the front face, the hole is arranged in the innerportion, the hole penetrates the ridge in part of a circumferentialdirection, the axial member is made of an aluminum alloy and has a frontend protruding frontward from the hole, the protruding portion spreadsoutward in a radial direction to form a flared portion, the rear face ofthe flared portion is in contact with the flange member on the peripheryof the hole, a portion of the axial member to the rear of the holeexpands outward in a radial direction to form a protrusion, and theflange member is held between the flared portion and the protrusion.

When an inner portion of the flange member partially has a ridge, theflange member has a higher rigidity and thereby reduce or avoiddistortion in the inner portion during electromagnetic forming. Thisenables the mounting face of the outer portion to agree with the shapeof the mating face of a counter member satisfactorily. In addition, theridge serves to reduce or avoid distortion of the flange member due toload when the axial member with flange is attached to a counter member.Even when the ridge is formed by thickening part of the inner portion,the configuration does not substantially deteriorate the advantages ofweight reduction by using an aluminum alloy. This is because the entireflange member is not thickened.

Furthermore, an axial member with flange having low cost and a lightweight can be obtained by forming the flange member and the axial memberfrom an aluminum alloy extrudate.

In the above configurations, when viewed from the hole of the flangemember, the side toward the axial flange is defined as “front(forward)”, and an opposite side is defined as “rear (backward)”. So, aplane facing forward is defined as “front (front face)” and a planefacing backward is defined as “rear (rear face)”.

The front of the ridge together with the mounting face is preferably inaccordance with the shape of the mating face of the counter member. Inthis case, if the mating face is a plane, the mounting face is soarranged to be in the same plane with the front of the ridge.

In the axial member with flange, an inner portion of the flange membercan be thickened in a region where the ridge is arranged, i.e., theridge protruding frontward can be formed as a result of thickening.Alternatively, the entire inner portion can protrude frontward in itscross section, i.e., a ridge is arranged in the front and a groove isformed in the rear. The inner portion can have plural ridges.

The present invention further provides axial member with flange,including: a flange member having a through hole at a center partthereof and having a mounting face on the outer periphery of the hole,the mounting face being to be in contact with a mating face of anothermember; and an axial member being made of a tubular aluminum alloy,being inserted into the hole, being expanded by electromagnetic formingso as to be in intimate contact with the inner periphery of the hole,and being joined to the flange member, wherein the flange membercomprises two sheet members each made of an aluminum alloy extrudate,the two sheet members are overlaid with each other so that theirextrusion directions intersect with each other, and the hole is arrangedat the intersection, and wherein the axial member has a protrusionprotruding frontward from the hole, the protrusion spreads outward'in aradial direction to form a flared portion, a portion of the axial memberto the rear of the hole bulges outward in a radial direction to form aprotrusion, and the flange member is held between the flared portion andthe protrusion.

The axial member with flange having the above configuration can reduceor avoid distortion of the flange member during electromagnetic forming,since the flange member is made of two sheet members which are overlaidwith each other so that their extrusion directions intersect with eachother, and this increase the rigidity of the flange member, especiallythe rigidity of its cutting faces. This configuration prevents themounting face of the flange member from having a shape not agreeing withthe shape of the mating face of a counter member. In addition, theconfiguration can reduce or avoid distortion of the flange member due toload when the axial member with flange is mounted to a counter member.The sheet members can have a relatively small thickness at theoverlaying portion. In this case, the total weight of the flange memberdoes not increase so much even though two sheet members are used, andthe advantages of weight reduction by using an aluminum alloy are notdeteriorated.

The present invention further provides a connection member including:first and second flange members each having a mounting face to be incontact with a mating face of another member, the first and secondflange members being arranged at a distance from each other; a hollowmember comprising a pair of ribs connecting the first and second flangemembers; and an axial member comprising a tubular aluminum alloymaterial and having both ends fixed to the first and second flangemembers, respectively, wherein the first and second flanges each have ahole between the pair of ribs, the two ends of the axial member areinserted into the holes and are expanded by electromagnetic forming soas to be in intimate contact with the inner peripheries of the holes,respectively.

The connection member having the above configuration enables the axialmember to be fixed to the flange members securely without inviting anextra increase in weight and prevents, for example, misregistration ofthe axial member. Forming holes for fixing the axial member in the firstand second flange members also contributes to weight reduction. When thepresent invention is applied to a bumper stay, the axial member isreinforced. Thus, the rib is prevented from buckling (inclination) uponcollision, and the axial member deforms in the form of bellows tothereby increase the energy absorption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a bumper stay according to thepresent invention.

FIG. 2 is a cross sectional view illustrating a method for producing thebumper stay of FIG. 1 by electromagnetic forming.

FIG. 3 is a cross sectional view of a mould for electromagnetic formingfor use in the method just mentioned above.

FIG. 4 is a cross sectional view of another bumper stay according to thepresent invention.

FIG. 5 is a cross sectional view of yet another bumper stay according tothe present invention.

FIG. 6 is a cross sectional view of another bumper stay according to thepresent invention.

FIG. 7 is a cross sectional view of a tubular member with flangeaccording to the present invention.

FIG. 8 is a cross sectional view of yet another bumper stay according tothe present invention.

FIG. 9 is a cross sectional view of another tubular member with flangeaccording to the present invention.

FIG. 10 is a cross sectional view illustrating a method for producingthe tubular member with flange of FIG. 9 by electromagnetic forming.

FIG. 11 is a perspective view of an axial member with flange accordingto the present invention.

FIG. 12 is a cross sectional view taken along line A-A in FIG. 11.

FIG. 13 is a cross sectional view taken along line B-B in FIG. 11.

FIG. 14 is a perspective view of a flange member of the axial memberwith flange illustrated in FIG. 11.

FIG. 15 is a perspective view of another embodiment of the axial memberwith flange according to the present invention.

FIG. 16 is a cross sectional view taken along line C-C in FIG. 15.

FIG. 17 is a perspective view of yet another embodiment of the axialmember with flange according to the present invention.

FIG. 18 is a perspective view of a flange member of the axial memberwith flange illustrated in FIG. 17.

FIG. 19 is a perspective view (rear side) of an axial member with flangeas yet another embodiment according to the present invention.

FIG. 20 is a perspective view (rear side) of the flange member of theaxial member with flange illustrated in FIG. 19.

FIG. 21 is a perspective view of an axial member with flange as stillanother embodiment according to the present invention.

FIG. 22 is a cross sectional view taken along line D-D in. FIG. 21.

FIG. 23 is a perspective view of the flange member of the axial memberwith flange illustrated in FIG. 21.

FIG. 24 is a perspective view of an axial member with flange as anotherembodiment according to the present invention.

FIG. 25 is a cross sectional view taken along line E-E in FIG. 24.

FIG. 26 is a cross sectional view of a connection member according tothe present invention in a plane passing through the center of a throughhole of a flange.

FIG. 27 is a plan view of the flange used in the above connectionmember.

FIG. 28 is a perspective view of another connection member according tothe present invention.

FIG. 29 is a plan view of a flange used in the above connection member.

FIG. 30 is a cross sectional view of another connection member accordingto the present invention in a plane perpendicular to the extrusiondirection and passing through the center of a through hole of a flange.

FIG. 31 is a partially sectional perspective view of a connection memberaccording to the present invention when used as a bumper stay.

FIG. 32 is a partially sectional perspective view of another connectionmember according to the present invention when used as a bumper stay.

FIG. 33 is a partially sectional perspective view of yet anotherconnection member according to the present invention when used as abumper stay.

FIG. 34 is a cross sectional view of another connection member accordingto the present invention in a plane perpendicular to the extrusiondirection and passing through the center of a through hole of a flange.

FIG. 35 is a plan view of a flange used in the above connection member.

FIG. 36 is a cross sectional view of the above flange in a planeperpendicular to the extrusion direction.

FIG. 37 comprises a cross sectional view FIG. 37( a) and a partiallyenlarged view FIG. 37( b) thereof, respectively, of another connectionmember according to the present invention in a plane perpendicular tothe extrusion direction and passing through the center of a through holeof a flange.

FIG. 38 is a cross sectional view of another connection member accordingto the present invention in a plane perpendicular to the extrusiondirection and passing through the center of a through hole of a flange.

FIG. 39 is a cross sectional view of another untreated pipe for use inthe present invention.

FIG. 40 is a cross sectional view of another flange for use in thepresent invention in a plane perpendicular to the extrusion direction.

FIG. 41 is a cross sectional view of another connection member accordingto the present invention in a plane perpendicular to the extrusiondirection and passing through the center of a through hole of a flange.

FIG. 42 is a perspective view of an axial member with flange accordingto the present invention.

FIG. 43 is a cross sectional view taken along line A-A in FIG. 42.

FIG. 44 is a cross sectional view taken along line B-B in FIG. 42.

FIG. 45 comprises end views FIG. 45( a) and FIG. 45( b) of a sheetmember, and a perspective view FIG. 45( c) of a flange member, for usein the axial member with flange illustrated in FIG. 42.

FIG. 46 is a perspective view illustrating a sheet member as anotherembodiment according to the present invention, and a method of cuttingthe sheet member.

FIG. 47 is a plan view of a flange member using the sheet member justmentioned above.

FIG. 48 comprises end views FIG. 48( a) and FIG. 48( b) of a sheetmember, and a perspective view FIG. 48( c) of a flange member, for usein an axial member with flange according to another embodiment of thepresent invention.

FIG. 49 comprises a cross sectional view FIG. 49( a) taken along lineC-C and a cross sectional view FIG. 49( b) taken along line D-D in FIG.48( c).

FIG. 50 comprises end views FIG. 50( a) and FIG. 50( b) of a sheetmember, and a perspective view FIG. 50( c) of a flange member, for usein an axial member with flange according to yet another embodiment ofthe present invention.

FIG. 51 is a perspective view of a bumper stay according to the presentinvention.

FIG. 52 is a perspective view of a hollow member constituting the bumperstay just mentioned above.

FIG. 53 is a cross sectional view illustrating a production method ofthe bumper stay.

FIG. 54 is a cross sectional view taken along line I-I in FIG. 51.

FIG. 55 is a cross sectional view taken along line II-II in FIG. 51.

FIG. 56 is a cross sectional view of another bumper stay according tothe present invention.

FIG. 57 is perspective view of yet another bumper stay according to thepresent invention.

FIG. 58 is across sectional view taken alone line in FIG. 57.

FIG. 59 is a perspective view of another bumper stay according to thepresent invention.

FIG. 60 is a cross sectional view taken along line IV-IV in FIG. 59.

FIG. 61 is a perspective view of another bumper stay according to thepresent invention.

FIG. 62 is a plan view of one of members constituting a hollow member ofthe bumper stay just mentioned above.

FIG. 63 is a plan view of the other of members constituting a hollowmember of the bumper stay just mentioned above.

FIG. 64 is across sectional view illustrating a production method of theabove bumper stay.

FIG. 65 is a perspective view of a bumper stay according to the presentinvention.

FIG. 66 is a perspective view of a flange member constituting the bumperstay just mentioned above.

FIG. 67 is across sectional view illustrating a production method of thebumper stay just mentioned above.

FIG. 68 is a cross sectional view taken along line I-I in FIG. 65.

FIG. 69 is a cross sectional view taken along line II-II in FIG. 65.

FIG. 70 is a cross sectional view of another bumper stay according tothe present invention.

FIG. 71 is a cross sectional view taken along line in FIG. 70.

FIG. 72 is a perspective view of yet another bumper stay according tothe present invention.

FIG. 73 is a plan view of one of members constituting a flange member ofthe bumper stay just mentioned above.

FIG. 74 is a plan view of the other of members constituting a flangemember of the bumper stay just mentioned above.

FIG. 75 is a cross sectional view illustrating a production method ofthe bumper stay just mentioned above.

FIG. 76 is a cross sectional view of still another bumper stay accordingto the present invention.

FIG. 77 comprises a plan view FIG. 77( a) before burring and a side viewFIG. 77( b) after burring, respectively, of another embodiment of themember constituting the flange member of the bumper stay illustrated inFIG. 76.

FIG. 78 is a cross sectional view of another embodiment of the memberconstituting the flange member of the bumper stay illustrated in FIG.76.

FIG. 79 comprises plan views illustrating various bumper stays and themounting thereof.

FIG. 80 is a cross sectional view illustrating a production method ofthe bumper stay illustrated in FIG. 79( c) by electromagnetic forming.

FIG. 81 is an enlarged cross sectional view of the flange of the bumperstay just mentioned above.

FIG. 82 is a cross sectional view illustrating the mounting of thebumper stay to a bumper reinforcement.

FIG. 83 is a cross sectional view of an example of conventionalelectromagnetic expansion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The axial members with flange according to the present invention will beillustrated with reference to FIGS. 1 to 10 by taking bumper stays as anexample.

A bumper stay illustrated in FIG. 1 comprises an axial member 21 and aflange member 22. The axial member 21 is made of a tubular aluminumalloy extrudate. The flange member 22 is joined to the both ends of theaxial member 21. The axial member 21 has end flanges (flared portions)23 at its both ends. The end flanges 23 are integral with the axialmember 21 and have an outer diameter less than that of the flange member22. The axial member 21 has the minimum diameter in the vicinity of anend of an axial direction to constitute a small-diameter portion 24, andprotrudes outward in a radial direction inside the small-diameterportion 24 to constitute a large-diameter portion (protrusion) 25. Theflange member 22 has a hole 26 at its center part, into which the axialmember 21 is to be inserted, and a cylindrical hole flange 27 at the rimof the hole 26. The axial member 21 is inserted into the hole 26 of theflange member 22, the end flange 23 is in intimate contact with and laidupon the outer face of the flange member 22, and the end 25 a of theprotruding large-diameter portion 25 is in contact with the end of thehole flange 27. Consequently, the hole flange 27 is held between the endflange 23 and the large-diameter portion 25. The outer periphery of thesmall-diameter portion 26 is in intimate contact with the innerperiphery of the hole flange 27.

In addition, the flange member 22 has a riser or ramp 28 having a stepheight substantially equal to the thickness of the end flange 23 so thatthe end flange 23 properly fits in a depression in the inner radius.Consequently, the outer face of the end flange 23 of the axial member 21is flush with (has the same height as) a portion of the outer face ofthe flange member 22 where not lying on the end flange 23.

A production method (electromagnetic forming method) of the bumper staywill be illustrated with reference to FIGS. 2 and 3.

A flange member 22 has the same shape as the flange member illustratedin FIG. 1 and can be produced by drilling a pilot hole at the center ofa circular blank (sheet material) while forming an annular riser or ramp28, and burring the pilot hole to thereby form a cylindrical hole flange27.

An untreated pipe 31 for use in electromagnetic forming comprises analuminum alloy extrudate having an outer diameter equal to or slightlysmaller than the inner diameter of the hole flange 27.

A mould 32 for use in electromagnetic forming comprises plural dividedmoulds which are vertically divided. When they are integrated, a throughhole 33 is formed at the center thereof, as illustrated in FIGS. 2 and3. The through hole 33 has a smaller diameter in a region in thevicinity of both ends of the mould 32 in an axial directioncorresponding to the length of the hole flange 27 (a small-diameterportions 33 a). The inner diameter of the small-diameter portion 33 a isset substantially equal to the outer diameter of the hole flange 27 sothat the hole flange 27 properly fits. The through hole 33 has a largerdiameter in a region (large-diameter portion 33 b) inside in an axialdirection of the small-diameter portions 33 a. The mould 32 has risersor ramps 34 a at both end faces 34 so that the flange member 22 properlyfits into the end face 34.

With reference to FIG. 2, the flange member 22 is placed on the both endfaces 34 of the mould 32 so that the hole flange 27 faces inward in anaxial direction, and the untreated pipe 31 is inserted into the holeflange 27. In this procedure, both ends of the untreated pipe 31 areprotruded to predetermined lengths from the flange member 22. Theprotruding length is controlled so that the outer periphery of the endflange 23 after electromagnetic forming is positioned on the innerperiphery of the riser or ramp 28 of the flange member 27, as shown in.FIG. 1. Namely, the untreated pipe 31 is cut so that the protrudinglength becomes the above-specified length.

A current-carrying coil 35 for electromagnetic forming is then insertedinto the untreated pipe 31, and electric energy accumulated at highvoltage in an impulse current generator (not shown) is applied thereto.As a result, the untreated pipe 31 yields magnetic repulsive force andthereby instantaneously expands. The end of the untreated pipe 31protruding from the flange member 22 largely spreads and hits againstthe flange member 22. The untreated pipe 31 is pressed to the inner faceof the hole flange 27 in a portion corresponding to the small-diameterportion 33 a of the through hole 33, and hits against the inner face ofthe through hole 33 in a region corresponding to the large-diameterportion 33 b of the through hole 33. The current-carrying coil 35 forelectromagnetic forming comprises an electric insulator and a formingcoil embedded in the electric insulator.

The bumper stay illustrated in FIG. 1 is thus molded. After molding, themould 32 is divided and the bumper stay is taken out therefrom.

In this bumper stay, with expansion of the untreated pipe 31, the axialmember 21 in the small-diameter portion 24 after molding is pressed tothe hole flange 27, and simultaneously the hole flange 27 of the flangemember 22 is held in an axial direction by the axial member 21 betweenthe end flange 23 and the large-diameter portion 25 thereof.Consequently, the flange member 22 is securely joined to the both endsof the axial member 21. The flange member 22 is in contact with theaxial member 21 in a large area due to the hole flange 27, and this alsocontributes to increase in bonding strength. The flange member 22 has asufficient outer diameter as a bumper stay whereas the end flange 23 ofthe axial member 21 does not necessarily has an excessively large outerdiameter as a result of expansion. Thus, cracking upon electromagneticforming can be prevented, and an aluminum alloy extrudate having a fiberstructure can be used.

In the above example, the hole 26 of the flange member 22 is a roundhole. It can also has an elliptic shape or a non-centrosymmetric shape.Examples of such a non-centrosymmetric shape are a shape having an edgemost of which is round but part of which is concave, and a shape havingan edge most of which is round but part of which is linear. Such crosssectional shapes contribute to preventing the rotation between the axialmember 21 and the flange member 22. In any case, the untreated pipe mayhave a round cross sectional shape. Even when an untreated pipe having around cross sectional shape is used, the cross section of a portion ofthe pipe pressed to the inner face of the hole flange as a result ofelectromagnetic forming is in accordance with the shape of the hole.

The axial member 21 (untreated pipe 31) to be molded by electromagneticforming comprises an aluminum alloy extrudate having a high electricconductivity and serving to yield high magnetic repulsive force. Incontrast, the flange member 22 can comprise an aluminum alloy sheet or asteel sheet, since it is not substantially deformed. It preferablycomprises a steel sheet for easier burring. When a steel sheet is usedas the flange member 22, the steel sheet is preferably subjected tosurface treatment for preventing electrolytic corrosion, such asaluminum plating, at least on a side to be in contact with the axialmember 21. Thus, electrolytic corrosion caused as a result of contact ofthe steel sheet with an aluminum alloy, i.e. the axial member 21 will beprevented.

Such a steel sheet has high strength and yields substantially noexpansive force upon electromagnetic forming due to its low electricconductivity. Thus, electromagnetic forming may be carried out withoutusing the mould 32 if the flange member 22 made of a steel sheet hassuch a strength as to receive the expansive force upon expansion of theuntreated pipe 31 and contributes to reliable positioning in molding sas to prevent the flange member 22 typically from misregistration.

Next, other bumper stays and tubular members with flange according tothe present invention will be illustrated below.

A bumper stay shown in FIG. 4 is substantially the same as the bumperstay shown in FIG. 1, except that an axial member 21 is welded with aflange member 22 so as to join the two members more securely. A weldingspot 36 is located at an outer periphery of an end flange 23. Thewelding spot 36 is away in an outer diameter direction from an axialsection 37 of the axial member 21, which axial section 37 corresponds tothe small-diameter portions 24 and the large-diameter portion 25 inFIG. 1. Thus, the axial section 37 is prevented from decrease inmaterial properties induced by heat and from unexpectable decrease inenergy absorption.

A bumper stay shown in FIG. 5 has substantially the same configurationas the bumper stay shown in FIG. 1, except that a large-diameter portion(bead-like protrusion) 38 of an axial member 21 is arranged only in thevicinity of a hole flange 27. A small-diameter portion 24 of an axialsection 37 is pressed to a hole flange 27 while the hole flange 27 isheld between an end flange 23 and a large-diameter portion 38, and thusthe flange member 22 is securely joined to both ends of the axial member21, as in the bumper stay shown in FIG. 1.

In the production of the bumper stay shown in FIG. 5, an electromagneticforming mould 39 having a tubular depression 39 a in a regioncorresponding the large-diameter portion 38, as indicated by virtuallines, may be used. The untreated pipe freely expands (protrudes anddeforms) at the depression 39 a in accordance with the expansive forceapplied as a result of electromagnetic forming.

A bumper stay shown in FIG. 6 comprises an axial member 21 and a flangemember 22, which flange member 22 is joined to only one end of the axialmember 21. An end flange 41 integral with the axial member 21 is used asa mounting flange at the other end. Of mounting flanges of a bumperstay, one near to a side member must have a larger diameter and must bea flange member 22 as an independent component. However, the other onenear to a bumper reinforcement may have a relatively small diameter andmay be an end flange 41 formed by expanding an end of the axial member21. In this case, a bumper stay of this type can be used.

FIG. 6 illustrates an electromagnetic forming mould 42 and an untreatedpipe 31 indicated by virtual lines, which is used for the molding of theaxial member 21.

A tubular member with flange shown in FIG. 7 comprises an axial member51 and a flange member 22 being joined to one end of the axial member51. The flange member 22 has the same shape as the flange member 22shown typically in FIG. 1, but the axial member 51 has an end flange 52integrally arranged at one end thereof and has neither flange norprotrusion at the other end.

In the tubular member with flange, the axial member 51 is placed in ahole 26 of the flange member 22, the end flange 52 is in intimatecontact with and matches with the outer face of the flange member 22,and the outer periphery of an axial section 53 is in intimate contactwith the inner periphery of a hole flange 27. The flange member 22 has ariser or ramp 28 substantially corresponding to the thickness of the endflange 52. The end flange 52 fits in a depression inside in a radialdirection. The axial member 51 and the flange member 22 are welded at awelding spot 54 on the outer periphery of the end flange 52. The outerface of the end flange 52 of the axial member 51 is substantially flushwith a portion of the outer face of the flange member 22 where not lyingover the end flange 52.

The tubular member with flange has an advantage that the axial section53 is prevented from heat-induced decrease in material properties, sincethe welding spot 54 is away in an outer diameter direction from theaxial section 53 of the axial member 51, as in the bumper stay shown inFIG. 4.

To mold the tubular member with flange by electromagnetic forming, aflange member 22 is placed on an end face 57 of an electromagneticforming mould 56 (a virtual line in FIG. 7) so that a hole flange 27faces inward in an axial direction. Then, an untreated pipe 58 (avirtual line in FIG. 7) made of a tubular aluminum alloy extrudate isinserted into the hole flange 27. In this procedure, an end of theuntreated pipe 58 is protruded to a predetermined length from the flangemember 22. The protruding length is controlled in the same manner asdescribed with reference to FIG. 2. The end face 57 of the mould 56 hasthe same shape as the mould 32 shown in FIG. 3. The through hole of themould 56 has a large diameter in a region in the vicinity of the endface 57 corresponding to the length of the hole flange 27, and thediameter of the through hole in this region is substantially the same asthe outer diameter of the hole flange 27 so that the hole flange 27properly fits therein. In the other region, the through hole has adiameter substantially equal to or slightly larger than the outerdiameter of the untreated pipe 58.

Next, electromagnetic forming is carried out in the same manner asabove, and the untreated pipe 58 instantaneously expands. Consequently,the end of the untreated pipe 58 protruding from the flange member 22largely spreads and hits against the flange member 22. Inside thethrough hole of the mould 56, the untreated pipe 58 is pressed to theinner periphery of the hole flange 27 and to the through hole.

The end flange 52 may also be molded by pressing (pressing expansion).The axial member 51 may be inserted into the flange member 22 aftermolding the end flange 52 or, alternatively, the end flange may bemolded after inserting the untreated pipe 58 into the flange member 22.

A bumper stay shown in FIG. 8 comprises an axial member 61 and flangemembers 62 being joined to both ends of the axial member 61. The axialmember 61 has end flanges 63 integrally arranged at both ends. The endflange 63 has an outer diameter smaller than that of the flange member62. The axial member 61 has a minimum diameter in the vicinity of an endin an axial direction to constitute a small-diameter portion 64, has alarger diameter and protrudes outward in an outer diameter directioninside in an axial direction of the small-diameter portion 64, toconstitute a large-diameter portion 65. The flange member 62 has a hole66 at its center part, to which hole the axial member 61 is to beinserted. The axial member 61 is placed in the hole 66 of the flangemember 62. The end flange 63 is in intimate contact with the outer faceof the flange member 62, and an end 65 a of the protrudinglarge-diameter portion 65 is in contact with the inside of the flangemember 62. Consequently, the flange member 62 on the periphery of thehole 66 is held between the end flange 63 and the large-diameter portion65. The outer periphery of the small-diameter portion 64 is in intimatecontact with the inner rim of the hole 66. Specifically, the bumper stayshown in FIG. 8 differs from the bumper stay shown in FIG. 1 only inthat the flange member 62 has no hole flange 27 in contrast to theflange member 22 shown in FIG. 1, and along with this, the shape of theaxial member 61 differs from that of the axial member 21 shown in theFIG. 1. Also in this case, the axial member 61 and the flange member 62can be welded in the same manner as in FIG. 4.

FIG. 8 also illustrates an electromagnetic forming mould 67 and anuntreated pipe 68 by virtual lines.

A tubular member with flange shown in FIG. 9 comprises an axial member71 made of a tubular aluminum alloy extrudate, and a flange member 72joined to an end of the axial member 71. The axial member 71 has anannular protrusion 73 in the vicinity of the end. The flange member 72has a hole 74 at its center part, the entire edge of the hole 74 iscurved toward the axial member 71. The tip of the curved portion 75 fitsinto the protrusion 73 from the inside and is in contact with thebottom, while the outer periphery of the curved portion 75 is inintimate contact with the inner periphery of the axial member 71 at theend thereof.

A production method (electromagnetic forming method) of the tubularmember with flange will be illustrated with reference to FIG. 10.

An untreated pipe 76 is made of a cylindrical aluminum alloy extrudate.A flange material 77 comprises an aluminum alloy sheet with a hole 78 atits center part. The hole 78 has a diameter smaller than that of thehole 74. One face of the flange material 77 is in contact with an endface of the untreated pipe 76, and the hole 78 is located at the centerof the untreated pipe 76 in cross section. The flange material 77 has aportion inclined toward the untreated pipe 76 in the vicinity of theedge of the hole 78.

A mould for use in electromagnetic forming comprises a main mould 81 anda presser mould 82. The main mould 81 comprises plural moulds dividedvertically. When the divided moulds are integrated, a through hole 83 isformed at the center part, and an annular depression 83 a is formed inthe vicinity of an end of the through hole 83, as illustrated in FIG.10. The through hole 83 has an inner diameter substantially equal to theouter diameter of the untreated pipe 76, except for the depression 83 a.The presser mould 82 also has a through hole 84 at the center part.

With reference to FIG. 10, the untreated pipe 76 is inserted into themain mould 81 and is positioned so that an end face (upper end) thereofis substantially flush with an end face 85 of the main mould 81. Theflange material 77 is placed on the end face 85 of the main mould 81 andis pressed at its top by the presser mould 82. A current-carrying coil86 for electromagnetic forming is then inserted into the flange material77 and the untreated pipe 76, and an electric energy is applied. Thus,the periphery (a portion inside the cross section of the untreated pipe76) of the hole 78 of the flange material 77 and the untreated pipe 76instantaneously expand, the flange material 77 largely spreads in thevicinity of the edge of the hole 78 and hits against the inner peripheryof the untreated pipe 76 in the vicinity of the end. The vicinity of theend of the untreated pipe 76 protrudes into the depression 83 a to formthe protrusion 73. Consequently, a curved portion 75 is formed at theedge of a hole 74, the outer periphery of the curved portion 75 isbrought into intimate contact with the end inner periphery of the axialmember 71 while the curved tip of the curved portion 75 fits into theprotrusion 73 of the axial member 71 from the inside. Thus, the axialmember 71 and the flange member 72 are joined to each other.

The resulting tubular member with flange is free from cracking duringthe electromagnetic forming and may use an aluminum alloy extrudatehaving a fiber structure as the axial member 71. This is because thereis no need of expanding the axial member 71 and the flange member 72 somuch.

Other embodiments of the axial member with flange according to thepresent invention will be illustrated below, with reference to FIGS. 11to 25.

FIGS. 11 to 16 illustrate embodiments of the axial members with flange,in which the front of a flange member, specifically in a region aroundthe hole with which an axial flange is in contact with, is notaxisymmetric with respect to the axis of the axial member.

An axial member with flange 121 shown in FIG. 11 comprises a sheetflange member 122 and a tubular axial member 123 being joined to theflange member 122 at one end thereof. The flange member 122 is made ofan aluminum alloy extrudate and is formed by cutting the extrudate in aplane perpendicular to the extrusion direction to a predeterminedlength, as illustrated in FIG. 14 in which the line of cutting plane isindicated by a virtual line. The flange member 122 comprises right andleft outer portions 124, an inner portion 125, and right and left ramps126 connecting the inner portion 125 and the outer positions 124. Theouter portions 124 and the inner portion 125 are sheets in parallel withone another. The front faces of the outer portions 124 are locatedfrontward from the front face of the inner portion 125 and serve as amounting face to be in contact with a mating face (plane) of a countermember (not shown). The axial member 123 is vertically joined to theinner portion 125.

The flange member 122 is a sheet member having, as a whole, asubstantially uniform thickness but has a ridge 127 at the front centerpart of the inner portion 124. The ridge 127 has a rectangular crosssectional shape and a larger thickness than the other portions of theflange member 122. The flange member 122 also has a round hole 128 atthe center part of the inner portion 125, and the hole 128 penetratesthe ridge 127 in a thickness direction of the sheet partly in itscircumferential direction. Consequently, the inner periphery of the hole128 is high at the ridge 127 and is low in the other region.

The axial member 123 is made of an aluminum alloy extrudate having around cross sectional shape, and the untreated pipe (extrudate) is cutin a plane perpendicular to the extrusion direction to a predeterminedlength.

Materials for the flange member 122 preferably have a high strength anda low electric conductivity. Preferred examples thereof are T5 temperedmaterials specified in Japanese Industrial Standards (JIS) 5000 series,JIS 6000 series or JIS 7000 series. Materials for the axial memberpreferably exhibit satisfactory moldability and have a high electricconductivity. Preferred examples thereof are materials specified in JIS6000 series, such as one specified in JIS 6063. The axial member ispreferably made of an aluminum alloy extrudate but may be made of analuminum alloy sheet by bending.

The axial member with flange 121 is produced in the following manner.Initially, an untreated pipe 129 is inserted into a hole 128 of a flangemember 122 so that the front end of the untreated pipe 129 protrudesfrom the hole 128. The flange member 122 and the untreated pipe 129 arepositioned by a device (not shown), as illustrated in FIGS. 12 and 13.

Next, an electromagnetic forming coil (not shown) is inserted into theuntreated pipe 29, and electromagnetic forming is carried out.Consequently, with reference to FIGS. 11 to 13, the untreated pipe 129inside the hole 128 expands and comes into intimate contact with theinner periphery of the flange member 122 around the hole 128, theprotruding portion 129 a protruding frontward from the hole 122 spreadsoutward in a radial direction to form an axial flange (flared portion)131, and a rear end 131 a of the axial flange 131 hits against and comesinto intimate contact with the front face (including the front face ofthe ridge 127) of the inner portion 125 around the hole 128. Inaddition, the untreated pipe 129 near to the rear of the hole 128 bulgesoutward in a radial direction in accordance with the intensity of theexpansive force by the action of the repulsive force of the magneticfield to thereby form a protrusion 132.

In the resulting axial member with flange 121, an axial member 123 afterexpansion (the untreated pipe after molding is referred to as “axialmember 123) is in intimate contact with the inner periphery of theflange member 122 around the hole 128, the flange member 122 is heldfrom the front and the rear between the axial flange 131 and theprotrusion 132 in a region around the hole 128, and the ridge 127 iscrimped by the axial flange 131 in a horizontal direction (right andleft direction). The ridge 127 and the axial flange 131 engage with eachother and their relative rotation is prevented even if a force acts torotate the flange member 122 around the axis X of the axial member 123.

The front shape of the flange member 122 in a region around the hole 128with which the axial flange 131 is in contact will be explained in moredetail. Specifically, the front face of the flange member 122 in thisregion is in one plane perpendicular to the axis X of the axial member123, except for the ridge 127. The front face is not axisymmetric withrespect to the axis X due to the ridge 127, and this yields theengagement between the axial flange 131 and the flange member 122 (inthe ridge 127). As the flange member 122 is made of an extrudate, theridge 127 is also present in the other region than the region around thehole 128 where the axial flange 131 is in contact. However, the flangemember 122 (the ridge 127) does not engage with the axial flange 131 inthe other region, and whether or not the ridge 127 is present in theother region is not an issue to achieve the objects of the presentinvention.

The same advantages as above can be obtained when the flange member 122has a groove in its front instead of the ridge 127.

An axial member with flange 141 shown in FIG. 15 comprises a sheetflange member 142 and a tubular axial member 143 joined at an end to theflange member 142. The flange member 142 is made of an aluminum alloyextrudate and is formed by cutting the extrudate in a planeperpendicular to the extrusion direction to a predetermined length. Itcomprises right and left outer portions 144, an inner portion 145, andright and left inclined ramps (risers) 146 connecting the inner portion145 and the outer portions 144. The inner portion 145 has a round hole148 in its thickness direction. This flange member 142 corresponds tothe flange member 122 illustrated in FIG. 14, except for not having theridge 127 and having a flat plane as the front of the inner portion 125.The flange member 142 is a sheet member having a substantially uniformthickness as a whole. The front faces of the outer portions 144 serve asa mounting face to be in contact with a mating face of another member(not shown), as in the flange member 122. The axial member 143 isvertically joined to the inner portion 145.

The axial member 143 is made of an aluminum alloy extrudate and isformed by cutting an untreated pipe 149 in a plane perpendicular to theextrusion direction to a predetermined length, as shown in FIG. 16.

The axial member with flange 141 is produced in the same manner as theaxial member with flange 121. With reference to FIGS. 15 and 16, theaxial member with flange 141 is produced in the following manner. Insidethe hole 148, the untreated pipe 149 expands and comes into intimatecontact with the inner periphery of the flange member 142 around thehole 148. A protruding portion 149 a of the untreated pipe 149protruding frontward from the hole 148 spreads outward in a radialdirection to form an axial flange 151. The rear face of the protrudingportion 149 a hits against and comes into intimate contact with thefront of the inner portion 124 and partially to the inclined ramp 146around the hole 148. The untreated pipe 149 to the rear of the hole 148bulges outward in a radial direction in accordance with the intensity ofthe expansive force induced by the repulsive force of a magnetic fieldto form a protrusion 152.

In the axial member with flange 141, the expanded axial member 143 (theuntreated pipe after molding is referred to as “axial member 143”) is inintimate contact with the inner periphery of the flange member 142around the hole 148, and the flange member 142 is held, from the frontand the rear, between the axial flange 151 and the protrusion 152 aroundthe hole 128. The axial flange 151 is in contact both with the innerportion 145 and the inclined ramp 146 of the flange member 142. The ramp146 and the region of the axial flange 151 in contact with the riser orramp 146 together serve to latch the relative rotation between theflange member 142 and the axial member 143. This prevents the relativerotation between the flange member 142 and the axial member 143 even ifa force acts to rotate the flange member 142 around the axis X of theaxial member 143.

The front of the flange member 142, particularly in a region around thehole 148 with which the axial flange 151 is in contact, is notaxisymmetric with respect to the axis X of the axial member 143 due tothe presence of the ramp 146 in the region, although the front face ofinner portion 145 is a plane perpendicular to the axis X of the axialmember 143. In addition, being not axisymmetric provides the engagementbetween the axial flange 151 and the flange member 142 (the ramp 146).

FIGS. 17 and 18 illustrate a specific configuration of an axial memberwith flange in which a hole in a flange member has a non-circular shapein an axial direction of the axial member.

An axial member with flange 161 illustrated in FIG. 17 comprises a sheetflange member 162 and a tubular axial member 163 to which end the flangemember 162 is joined. With reference to FIG. 18, the flange member 162is made of an aluminum alloy extrudate having the same cross section asthe flange member 142 and is formed by cutting the extrudate in a planeperpendicular to the extrusion direction to a predetermined length. Theflange member 162 is a sheet member having a substantially uniformthickness and comprises right and left outer portions 164, an innerportion 165 and right and left ramps 166 connecting the inner portion165 and the outer positions 164. The front faces of the outer portions164 serve as a mounting face to be in contact with a mating face ofanother member (not shown). The inner portion 165 has a hole 168 in itsthickness direction. Part of the round periphery of the hole 168protrudes outward in a radial direction as an arc to form protrusions168 a. The axial member 163 is vertically joined to the inner portion165.

The axial member with flange 161 is produced in the same manner as theaxial member with flange 121. In the axial member with flange 161, theexpanded axial member 163 comes into intimate contact with the innerperiphery, including the inner periphery of the protrusion 168 a, of theflange member 162 around the hole 168, and the flange member 162 is heldbetween the axial flange 171 and the protrusion 172 from the front andthe rear around the hole 168, as in the axial member with flange 121.Part of the axial member 162 bulges into the protrusion 168 a of thehole 168, and this allows the flange member 162 and the axial member 163to latch each other in the region. Thus, the relative rotation betweenthe flange member 162 and the axial member 163 can be prevented even ifa force acts to rotate the flange member 142 around the axis X of theaxial member 143.

Examples of such holes having a non-circular shape include not only ahole having a circular periphery part of which protrudes outward in aradial direction as in the hole 168, but also a hole having a circularperiphery part of which protrudes inward in a radial direction, a holehaving a circular periphery part of which is linear, such as in aracetrack, a hole having an elliptic shape as a whole, and other holeshaving various shapes.

FIGS. 19 and 20 illustrate an axial member with flange in which the rearof a flange member, particularly in the periphery of a hole, is notaxisymmetric with respect to the axis of an axial member.

An axial member with flange 181 illustrated in FIG. 19 comprises a sheetflange member 182 and a tubular axial member 183 to which end the flangemember 182 is joined. The flange member 182 is made of an aluminum alloyextrudate and is formed by cutting the extrudate in a planeperpendicular to the extrusion direction to a predetermined length. Withreference to FIG. 20, the flange member 182 comprises right and leftouter portions 184, an inner portion 185 and right and left ramps 186connecting the inner portion 185 and the outer portions 184. The frontfaces of the outer portions 184 serve as a mounting face to be incontact with a mating face of another member (not shown). The innerportion 185 has a ridge 187 at the center part on the rear side thereofand has a larger thickness in the ridge 187. The ridge 187 has arectangular cross sectional shape. The inner portion 185 also has around hole 188 at the center part thereof. The hole 188 partly in itscircumferential direction penetrates the ridge 187 in a thicknessdirection. The flange member 182 corresponds to the flange member 122illustrated in FIG. 14, except for not arranging the ridge 127 in thefront face but for arranging, instead of the ridge 127, the ridge 187 onthe rear face. The axial member 183 is made of an aluminum alloyextrudate and is vertically joined to the inner portion 185.

The axial member with flange 181 is produced in the same manner as inthe axial member with flange 121. In the axial member with flange 181 asin the axial member with flange 121, the expanded axial member 183 is inintimate contact with the inner periphery of the hole 188, and theflange member 182 is held from the front and the rear between an axialflange (not shown) and the protrusion 192 around the hole 188. Inaddition, the ridge 187 is crimped by the protrusion 192 in a horizontaldirection, since the protrusion 192 has bulged at different startingpoints in a region corresponding to the ridge 187 and other regions,namely, the protrusion 192 bulges in the other regions at a startingpoint residing to the front of that of the region corresponding to theridge 187. Thus, the ridge 187 and the protrusion 192 engage with andlatch each other and are thereby prevented from relative rotation evenif a force acts to rotate the flange member 182 around the axis X of theaxial member 183.

The rear face of the flange member 182 particularly around the outerperiphery of the hole 188 is in a plane perpendicular to the axis X ofthe axial member 183, except for the ridge 187. The rear face, however,is not axisymmetric with respect to the axis X of the axial member 183due to the presence of the ridge 187, and being not axisymmetricprovides the engagement between the protrusion 192 and the flange member182 (ridge 187). As the flange member 182 is made of an extrudate, theridge 187 is also present in the other region than the region around theperiphery of the hole 188. However, the flange member 182 (the ridge187) does not engage with the protrusion 192 in the other region, andwhether or not the ridge 187 is present in the other region is not anissue to achieve the objects of the present invention.

Similar advantages as above can be obtained by arranging a groove orgrooves instead of the ridge 187 in the rear face of the flange member182.

FIGS. 21 to 25 illustrate axial members with flange, in which the frontof a flange member, particularly in a region around a hole with which anaxial flange is to be in contact, is not axisymmetric with respect tothe axis of an axial member, and the rear of the flange member, inparticular on the periphery of the hole, is not axisymmetric withrespect to the axis of the axial member.

An axial member with flange 201 illustrated in FIG. 21 comprises a sheetflange member 202 and a tubular axial member 203 to which end the flangemember 202 is joined. The flange member 202 is made of an aluminum alloyextrudate and is formed by cutting the extrudate in a planeperpendicular to the extrusion direction to a predetermined length. Withreference to FIG. 23, the flange member 202 comprises right and leftouter portions 204, an inner portion 205, and right and left ramps 206connecting the inner portion 205 and the outer portions 204. The frontfaces of the outer portions 204 serve as a mounting face to be incontact with a mating face of another member (not shown). The flangemember 202 has a substantially uniform thickness as a whole but has aridge 207 at a center part of the inner portion 205. The ridge 207protrudes frontward and forms a groove 209 when viewed from the rear.The inner portion 205 has a round hole 208 at the center part thereof,and the hole 208 partly in a circumferential direction penetrates theridge 207 in a thickness direction. In the illustrated example, theheight of the front face of the ridge 207 is set to be equal to that ofthe outer portions 204. The axial member 203 is made of an aluminumalloy extrudate and is vertically joined to the inner portion 205.

The axial member with flange 201 is produced in the same manner as theaxial member with flange 121, except that an untreated pipe (not shown)is positioned so that its front end agrees with the front face of theridge 207. In the axial member with flange 201 as in the axial memberwith flange 121, the expanded axial member 203 is in intimate contactwith the inner periphery of the hole 208, and the flange member 202 ispinched from the front and the rear between the axial flange 211 and theprotrusion 212 around the hole 208. The ridge 207 is crimped and held bythe flange 211 in a horizontal direction in the front side of the flangemember 202. The protrusion 212 in the rear side of the flange member 202bulges into the groove 209, since the protrusion 212 has bulged atdifferent starting points in a region corresponding to the groove 209and in the other region. Namely, the protrusion 212 has bulged at astarting point in the other region residing to the front of that of theregion corresponding to the groove 209. On the front of the flangemember 202, the ridge 207 and the axial flange 211 engage with and latcheach other, and on the rear thereof, the groove 209 and the protrusion212 engage with and latch each other. Thus, the relative rotationbetween these members is prevented even if a force acts to rotate flangemember 202 around the axis X of the axial member 203.

The front of the flange member 202, particularly in a region around thehole 208 with which the axial flange 211 is to be in contact, is in aplane perpendicular to the axis X of the axial member 203, except forthe ridge 207. The front is, however, not axisymmetric with respect tothe axis X of the axial member 203 because of the presence of the ridge207, and being not axisymmetric provides the engagement between theaxial flange 211 and the flange member 202 in the ridge 207. The rear ofthe flange member 202, particularly in the periphery of the hole 208, isnot axisymmetric with respect to the axis X of the axial member 203 dueto the presence of the groove 209, and this yields the engagementbetween the protrusion 212 and the flange member 202 (the groove 209).

An axial member with flange 221 illustrated in FIG. 24 comprises a sheetflange member 222 and a tubular axial member 223 to which end the flangemember 222 is joined. The flange member 222 is made of an aluminum alloyextrudate having the same cross section as the flange member 142 and isformed by cutting the extrudate in a plane perpendicular to theextrusion direction to a predetermined length. The flange member 222comprises right and left outer portions 224, an inner portion 225, andright and left ramps 226 connecting the inner portion 225 and the outerportions 224. The front faces of the outer portions 224 serve as amounting face to be in contact with a mating face of another member (notshown). The axial member 223 is joined to the inner portion 225 in aslanting direction.

The axial member 223 is made of an aluminum alloy extrudate having acircular cross section. With reference to FIG. 25, the front end of anuntreated pipe 229 is cut in a plane inclined with respect to a planeperpendicular to the extrusion direction, and the rear end thereof iscut in a plane perpendicular to the extrusion direction.

The axial member with flange 221 is produced substantially in the samemanner as the axial member with flange 121, except that flange member222 is positioned as being inclined with respect to a planeperpendicular to the axis X of the untreated pipe 229 (or the axialmember 223), as illustrated in FIG. 25. The inclination is set so thatthe front face of the inner portion 225 is in parallel with the frontend of the protruding untreated pipe 229. The hole 228 formed in theinner portion 225 has a circular shape when viewed from a direction ofthe axis X.

The axial member with flange 221 is produced in the following manner asillustrated in FIGS. 24 and 25. The untreated pipe 229 inside the hole228 expands and comes into intimate contact with the inner periphery ofthe flange member 222 around the hole 228. A protruding portion 228 a ofthe untreated pipe 229 protruding frontward from the hole 228 spreadsoutward in a radial direction to thereby form an axial flange 231. Theuntreated pipe 229 to the rear of the hole 228 bulges outward in aradial direction in accordance with the intensity of expansive forceinduced by the repulsive force of a magnetic field, to thereby form aprotrusion 232.

In the axial member with flange 221, the expanded axial member 223 (theuntreated pipe after molding is referred to as “axial member 223”) is inintimate contact with the inner periphery of the hole 228, and theflange member 222 is held from the front and the rear between the axialflange 231 and the protrusion 232 around the hole 228. In the axialmember 221, the flange member 222 (inner portion 225) is inclined withrespect to a plane perpendicular to the axis X of the axial member 223,and the flange member 222 and the axial member 223 latch each other soas to prevent the relative rotation between them. Accordingly, therelative rotation of the two members is prevented even if a force actsto rotate the flange member 222 around the axis X of the axial member223.

The front of the flange member 222, particularly in a region around thehole 228 with which the axial flange 231 is to be in contact,constitutes a plane inclined with respect to the axis X of the axialmember 223. Thus, the front of the flange member 222 is not axisymmetricwith respect to the axis X of the axial member 223. This yields relativelatching between the axial flange 231 and the flange member 222. Therear of the flange member 222, particularly in the periphery of the hole228, is in a plane in parallel with the front thereof, but the plane isinclined with respect to the axis X of the axial member 223. Thus, therear of the flange member 222 is not axisymmetric with respect to theaxis X of the axial member 223, and this yields relative latchingbetween the protrusion 232 and the flange member 222.

Connection members (axial members with flange) according to the presentinvention will be illustrated in detail with reference to FIGS. 26 to41.

A connection member 315 illustrated in FIG. 26 comprises two sheetflanges 311 and a tubular axial member 314 being joined to the flanges311 at both ends. The flange 311 as illustrated in FIG. 27 comprises aninner radius 318 around a through hole 312, an intermediate portion 320,and an outer radius 319. The inner radius 318 has a thickness largerthan that of the outer radius 319. The intermediate portion 320constitutes a ramp for smoothly connecting steps formed between theinner radius 318 and the outer radius 319. The inner radius 318 and theouter radius 319 have a step height therebetween. Namely, the front face318 a of the inner radius 318 is positioned to the rear of the frontface 319 a of the outer radius 319. The axial member 314 is made of analuminum alloy extrudate. Suitable example of the material therefor areJIS 6000 series materials such as JIS 6063 material. The material forthe flanges 311 preferably has a high strength and a low electricconductivity. Among aluminum alloys, T5 tempered materials such as JIS5000 series material, JIS 6000 series materials, and JIS 7000 seriesmaterials are preferred. Other materials such as steel materials canalso be employed.

The connection member 315 is produced in the following manner.Initially, the flanges 311 are positioned at a predetermined distance bya device (not shown). An untreated pipe 313 having a circular crosssection and being indicated by a virtual line is inserted through athrough hole 312 so that both ends thereof protrude frontward. Anelectromagnetic forming coil (not shown) is placed into the untreatedpipe 313, and electromagnetic forming is carried out. Thus, theuntreated pipe 313 expands and comes into intimate contact with theinner surface of the flange 311 around the through hole 312 inside theplane of the flange 311. The protruding portion 313 a of the untreatedpipe 313 to the front of the flange 311 spreads outward in a radialdirection, and the rear face of the protruding portion 313 a hitsagainst and comes into intimate contact with the front face 318 a of theflange 311 in the inner radius. The untreated pipe 313 inside the flange311 bulges outward in a radial direction and protrudes between theflanges 311 and 311 in accordance with the intensity of expansive forceinduced by the repulsive force of a magnetic field. This makes theflange 311 at the inner surface of the through hole 312 come intointimate contact with the axial member 314 and simultaneously be pinchedfirmly between the spread flared portion (axial flange) 316 and theinner protrusion 317 of the axial member 314. Thus, the flanges 311 arejoined to the axial member 314. The step height between the inner radius318 and the outer radius 319 of the flange 311 is set substantiallyequal to the wall thickness of the axial flange 316, which is in turnsubstantially equal to the wall thickness of the untreated pipe 313.Consequently, the front face 316 a of the axial flange 316 issubstantially flush with the front face 319 a of the outer radius 319.This configuration is advantageous when the flange 311 is used formounting to another member. The step height can also be set so that thefront face 316 a of the axial flange 316 is somewhat to the rear offront face 319 a of the outer radius 319.

In the above example, the through hole 312 of the flange 311 has acircular shape, but it can also have another shape than a circularshape, such as an elliptic shape or a polygonal shape. Such anon-circular shape prevents the rotation of the axial member in thethrough hole. The untreated pipe 313 (axial member 314) may have notonly a circular cross sectional shape but also a non-circular profilesuch as an elliptic shape or a polygonal shape.

A connection member 325 illustrated in FIG. 28 comprises a sheet flange321 and a tubular axial member 324 to which end the flange 321 isjoined. With reference to FIG. 29, the flange 321 is made of an aluminumalloy extrudate and is formed by cutting the extrudate in a planeperpendicular to the extrusion direction where the line of cutting planeis indicated by a virtual line. The flange 321 comprises a center part328, intermediate portions 330, and two side portions 329. The centerpart 328 has a larger thickness than those of the two side portions 329in a cross section perpendicular to the extrusion direction. Theintermediate portions are inclined so as to smoothly connecting stepsformed between the center part 328 and the side portions 329. The centerpart 328 has a step height with respect to the side portions 329.Namely, the front face 328 a of the center part 328 is positioned to therear of the front faces 329 a of the side portions 329. The center part328 has a round through hole 322 at its center.

The connection member 325 is produced in the same manner as in theconnection member 315, except for expanding an untreated pipe having acircular cross section only in the vicinity of the flange 321 byelectromagnetic forming instead of expanding the untreated pipethroughout its length. Consequently, the axial member 324 has an axialflange 326 to the front of the flange 321 and has a protrusion 327 tothe rear of the flange 321, but it has a diameter equal to that of theuntreated pipe in a region 331 to the rear of the protrusion 327 of theaxial member 324. In this connection, the axial flange 326 is to be incontact with the front face 328 a of the center part 328 of the flange321, as illustrated in FIG. 28. In the connection member 325, the frontface 326 a of the axial flange 326 is substantially flush with the frontfaces 329 a of the side portions 329, since the step height between thecenter part 328 and the side portions 329 of the flange 321 is set to besubstantially equal to the wall thickness of the axial flange 326, whichis in turn substantially equal to the wall thickness of the untreatedpipe. The step height may be set so that the front face 326 a of theaxial flange 326 is positioned somewhat to the rear of the front face329 a of the outer radius 329.

A connection member 345 illustrated in FIG. 30 has the sameconfiguration as the connection member 325, except that a rear face 341b of a flange 341 has a ramp (slope) so that a front face 341 a isformed as a plane as a whole. In this case, a spread axial flange 346 ofthe axial member 344 protrudes frontward from the front face 341 a ofthe flange 341. A connection member of this type may be producedaccording to necessity. The connection member 345 is the same as theconnection member 325 in that the flange 341 is made of an aluminumalloy extrudate. In addition, it is produced in the same manner.

The virtual line in FIG. 30 represents an untreated pipe 43 having acircular cross section.

FIG. 31 is an illustration of the connection member 325 used as a bumperstay. The side portions 329 of the flange 321 each have openings and arefixed to a bumper reinforcement 308 by means of bolts (not shown) tothereby constitute a bumper structure. The openings are preferablyformed before joining. Where necessary, a flange may be joined to sidemembers at the rear end (not shown) of the axial member 324 in the sameway as in the flange 321.

A connection member 355 illustrated in FIG. 32 differs from theconnection member 325 in that a flange 351 has a larger width in a crosssection perpendicular to the extrusion direction. When the connectionmember 325 is fixed to the bumper reinforcement 38 so that the extrusiondirection of the flange 321 lies in a horizontal direction as shown inFIG. 31, the flange 321 is limited in width, and the interval S betweenbolt openings is inevitably narrow. In contrast, when the connectionmember 355 is fixed to a bumper reinforcement 38 so that the extrusiondirection of the flange 351 lies in a vertical direction, the flange 351can have a large width, and thereby the interval S between bolt openingsis wide. This is advantageous for higher mounting strength.

A connection member 365 illustrated in FIG. 33 differs from theconnection member 325 in that a flange 361 has curved ends 368 rangingto side portions 369. In the connection member 365 as illustrated inFIG. 33, the front faces of the side portions 369 are brought intocontact with the rear face of a bumper reinforcement 38, the innersurfaces of the curved ends 368 are brought into contact with the upperand lower faces of the bumper reinforcement 38, and the curved ends 368are fixed to the bumper reinforcement 38 by means of bolts (not shown).

A connection member 375 illustrated in FIG. 34 comprises a sheet flange371 and a tubular axial member 374 to which end the flange 371 isjoined. With reference to FIGS. 35 and 36, the flange 371 is made of analuminum alloy extrudate and is formed by cutting the extrudate in aplane perpendicular to the extrusion direction. The flange 371 comprisesa center part 378, an intermediate portion 379 around the center part378, and a side portion 380 outside the intermediate portion 379. Theintermediate portion 379 has a larger thickness than that of the centerpart 378 and the side portion 380 in a cross section perpendicular tothe extrusion direction. The intermediate portion 379 is inclined so asto connect the center part 378 and the side portion 380. The center part378 has a step height with respect to the side portions 380. Namely, thefront face 378 a of the center part 378 is positioned to the rear of thefront faces 380 a of the side portions 380. The front face 379 a of theintermediate portion 379 intersects with the front face 378 a of thecenter part 378 at an obtuse angle.

The rear face 379 b of the intermediate portion 379 has an angularprojection 379 c protruding rearward from the rear face 378 b of thecenter part 378. The inner surface of the projection 379 c intersectswith the rear face 378 b at an obtuse angle. The center part 378 of theflange 371 has a round through hole 372. The through hole 372 has adiameter R somewhat smaller than the width L of the center part 378. Asthe through hole 372 is punched in the center part 378 having a smallthickness, a low pressing capability will do in the punching. Inaddition, working holes 382 are arranged around the through hole 372 atfour points so as to range over the center part 378, the intermediateportion 379 and the side portion 380, and bolt openings 383 are arrangedin the side portion 380.

The connection member 375 is produced so that an untreated pipe 373having a circular cross section is expanded not throughout its lengthbut only in the vicinity of the flange 371, as in the connection member325. With reference to FIG. 34, the resulting axial member 374 has anaxial flange 376 to the front of the flange 371 and a protrusion 377 tothe rear of the flange 371, but it keeps its original diameter as in theuntreated pipe in a region to the rear of the protrusion 377. Withreference to the axial flange 376 illustrated by a virtual line in FIGS.34 and 35, the rear face of the axial flange 376 is, in a major partthereof, in contact with the front face 378 a of the center part 378 ofthe flange 371 and is, in part in a circumferential direction mainly ina direction perpendicular to the extrusion direction, in contact withthe front face 379 a of the intermediate portion 379. The upper end 377a of the protrusion 377 is in contact with the inner surface of theprojection 379 c. The rear region 377 b of the protrusion 377 which isfree from the restriction by the projection 379 c expands and protrudesoutside in a radial direction in accordance with the intensity ofexpansive force induced by the repulsive force of a magnetic field.

In the connection member 375, the axial member 374 is pressed intointimate contact with the inner surface of the flange 371 around thethrough hole 372.

With reference to the sectional view of FIG. 34, right and left ends 378c of the center part 378 having a small thickness remain at both sidesof the through hole 372, and this makes axial member 374 be well engagedand come into intimate contact therewith more satisfactorily. To thefront of the ends 378 c, the axial flange 376 is in contact with thefront face 379 a of the intermediate portion 379 of the flange 371, andto the rear thereof, the upper end 377 a of the protrusion 377 is incontact with the inner surface of the projection 379 c. Thus, theintermediate portion 379 of the flange 371 is pinched between the axialflange 376 and the upper end 377 a of the protrusion 377. This enablesvery secure joining between the flange 371 and the axial member 374 andparticularly prevents disconnection of them in an axial direction. Theaxial flange 376 spreads at a varying angle along a circumferentialdirection, namely, it spreads partially at right angle but partially atan angle below 90 degrees. This prevents the rotation of the axialmember 374. In addition, applied energy in electromagnetic forming issaved, since part of the axial flange 376 spreads at an angle below 90degrees.

If the distance d between the through hole 372 and the working hole 382in a region 384 is set small, the region 384 deforms outward in a radialdirection due to expansive force of the axial member 372 duringelectromagnetic forming, and the axial member 374 enters the resultingdepression. This deformation prevents the rotation of the axial member374.

A connection member 395 illustrated in FIG. 37( a) comprises a sheetflange 391 and a tubular axial member 394 to which end the flange 391 isjoined. The flange 391 is made of an aluminum alloy extrudate and has,as its cross sectional structure, a thick intermediate portion 399 thatcomprises an inclined first intermediate portion 399 a, a horizontalsecond intermediate portion 399 b, and a substantially trapezoidalprojection 399 c to the rear thereof. The other configuration issubstantially the same as in the connection member 375. The flange 391is further effectively prevented from distortion and deformation duringelectromagnetic forming. This is because, the thick intermediate portion399 has a large width (the width in a horizontal direction in FIG. 37(a)) and ranges to the outside of a portion against which a spread axialflange 396 hits, namely to the horizontal portion (the secondintermediate portion 399 b). FIG. 37( a) also illustrates an untreatedpipe 393 having a circular cross section.

The flange 391 can be well engaged with and come into intimate contactwith the expanded axial member 394 more satisfactorily, since the flange391 has remaining thin ends 398 c of the center part 398 at both sidesof a through hole 392, as in the flange 371. The upper end 397 a of theprotrusion 397 is in contact with the projection 399 c so that theintermediate portion 399 of the flange 391 is pinched between the axialflange 396 and the upper end 397 a of the protrusion 397. This enablesvery secure joining between the flange 391 and the axial member 394. Thecorners between the center part 398 and the intermediate portion 399 inthe flange 391 (front corner 398 a and rear corner 398 b) are preferablyrounded as illustrated in FIG. 37( b), since shearing force will actthereon.

Other different configurations which the connection members, flanges,and axial members according to the present invention may have will beillustrated with reference to FIGS. 38 to 41.

A connection member 405 illustrated in FIG. 38 comprises a sheet flange401 made of an aluminum alloy extrudate, and a tubular axial member 404to which end the flange 401 is joined. The connection member 405 hassubstantially the same configuration as the connection member 395,except that the flange 401 has in its cross section no projectioncorresponding to the projection 399 c of the flange 391.

An untreated pipe 413 illustrated in FIG. 39 is used as an axial memberof a connection member. Both ends of the untreated pipe 413 which willconstitute axial flanges are thinned by cutting. The untreated pipe 413enables easy spreading and molding of axial flanges by electromagneticforming.

A flange 421 illustrated in FIG. 40 is made of an aluminum alloyextrudate and has a rib 423 at an end of a thin side portion 430. Therib 425 prevents the flange 421 from distortion upon electromagneticforming. The flange 421 has a gradually decreasing thickness in thethick intermediate portion 429 toward the outside.

A connection member 435 illustrated in FIG. 41 comprises a sheet flange431 and a tubular axial member 434 having a circular cross section towhich end the flange 431 is joined. The flange 431 is made of analuminum alloy extrudate and comprises a thick center part 438 and thinside portions 439. The center part 438 comprises a first center part 438a, an inclined second center part 438 b, and a third center part 438 c.With reference to the cross section illustrated in FIG. 41, the firstcenter part 438 a has a groove 433 in its inner surface. Uponelectromagnetic forming, the axial member 434 expands outward in aradial direction and fits into the groove 433. Thus, the axial member434 and the flange 431 are in intimate contact with each other furthersecurely.

Connection members according to the present invention will beillustrated in more detail with reference to FIGS. 42 to 50.

An axial member with flange 521 illustrated in FIG. 42 to FIG. 44comprises a sheet flange member 522 and a tubular axial member 523 towhich end the flange member 522 is joined. The flange member 522comprises two sheet members 524 and 525 overlaid with each other and hasa round hole 526 penetrating in a thickness direction at a center partthereof, as illustrated in FIG. 45. Each of the sheet members 524 and525 is made of an aluminum alloy extrudate and is formed by cutting theextrudate in a plane perpendicular to the extrusion direction to apredetermined length.

With reference to FIGS. 43 and 45, the front sheet member 524 has auniform thickness as a whole and comprises an inner portion 524 a, outerportions 524 b and 524 c at both ends, and intermediate portions 524 dand 524 e connecting these portions. The outer portions 524 b and 524 care in parallel with, but have a step height with the inner portion 524a. Thus, the outer portions 524 b and 524 c are positioned to the frontof the inner portion 524 a. With reference to FIGS. 44 and 45, the rearsheet member 525 has a uniform thickness as a whole and comprises aninner portion 525 a, outer portions 525 b and 525 c at both endsthereof, and intermediate portions 525 d and 525 e connecting theseportions. The outer portions 525 b and 525 c are in parallel with, buthave a step height with the inner portion 525 a. Thus, the outerportions 525 b and 525 c are positioned to the front of the innerportion 525 a. The step height between the outer portions 524 b and 524c and the inner portion 524 a in the sheet member 524 is set smallerthan the step height between the outer portions 525 b and 525 c and theinner portion 525 a in the sheet member 525.

In the flange member 522, the sheet member 524 is overlaid upon sheetmember 525 in their inner portion 524 a and 525 a so that the extrusiondirections intersect with each other perpendicularly, as illustrated inFIG. 45. The sheet member 524 has been cut so that the length L24 in theextrusion direction is equal to the width (front width) W525 of theinner portion 525 a of the sheet member 525. Likewise, the sheet member525 has been cut so that the length L525 in the extrusion direction isequal to the width (rear width) W524 of the inner portion 524 a of thesheet member 524. In the flange member 522 illustrated in FIG. 45, thesheet members 524 and 525 are overlaid with each other so that the frontfaces of the outer portions 524 b, 524 c, 525 b and 525 c are positionedin one plane. The front faces serve as a mounting face to be in contactwith a mating face (plane) of a counter member. When the axial memberwith flange 521 is used as a bumper stay, the counter member is a bumperreinforcement.

The axial member 523 is made of an aluminum alloy extrudate having acircular cross section and is formed by cutting an untreated pipe(extrudate) in a plane perpendicular to the extrusion direction to apredetermined length.

With reference to FIGS. 43 and 44, the axial member with flange 521 isproduced in the following manner. The sheet members 524 and 525 areoverlaid with each other to form the flange member 522. Next, anuntreated pipe 527 is inserted into the hole 526 of the flange member522 so that the front end of the untreated pipe 527 protrudes frontwardfrom the hole 526. The flange member 522 and the untreated pipe 527 arepositioned by a device (not shown). Next, an electromagnetic formingcoil (not shown) is placed in the untreated pipe 527 and electromagneticforming is carried out. Thus, with reference to FIGS. 42 to 44, theuntreated pipe 527 inside the hole 526 expands and comes into intimatecontact with the inner periphery of the flange member 522 around thehole 526. A protruding portion 527 a of the untreated pipe 527protruding frontward from the hole 526 spreads outward in a radialdirection to form a flared portion 528. The untreated pipe 527 to therear of the hole 526 bulges outward in a radial direction in accordancewith the intensity of expansive force induced by the repulsive force ofa magnetic field, to thereby form a protrusion 529.

In the axial member with flange 521, the expanded axial member 523 (theuntreated pipe after molding is referred to as “axial member 523”) is inintimate and secure contact with the inner periphery of the hole 526,and the flange member 522 around the hole 526 is pinched between theflared portion 528 and the protrusion 529 in a vertical direction (fromthe front of the sheet member 524 and from the rear of the sheet member525). This enables secure joining between the flange member 522 and theaxial member 523.

In addition, the sheet member 524 has an increased rigidity at cuttingplanes 524 f and 524 f. This is because the flange member 522 comprisesthe two sheet members 524 and 525 overlaid and intersecting with eachother; the cutting planes 524 f and 524 f of the sheet member 524 lieover the sheet member 525; and thereby a low rigidity of the sheetmember 524 at the cutting planes 524 f and 524 f are complemented(reinforced) by the rigidity of the sheet member 525. Likewise, thesheet member 525 has an improved rigidity at cutting planes 525 f and525 f as being complemented (reinforced) by the rigidity of the sheetmember 524. This reduces or avoids distortion of the axial member withflange 521 upon electromagnetic forming and also reduces or avoidsdistortion of the flange member 521 due to a load applied by a countermember, when the axial member with flange 521 is mounted to the countermember.

In the flange member 522, the cutting planes 524 f and 524 f of thesheet member 524 are positioned at a rigid end (at the corner formedwith the intermediate portions 525 d and 525 e) in the inner portion 525a of the sheet member 525 and are in parallel with the extrusiondirection of the sheet member 525. Likewise, the, cutting planes 525 fand 525 f of the sheet member 525 are positioned at a rigid end in theinner portion 524 a of the sheet member 524 (at the corner formed withthe intermediate portions 524 d and 524 e) and are in parallel with theextrusion direction of the sheet member 524. Consequently, the sheetmembers 524 and 525 highly make up in their rigidity for each other.Distortion is highly effectively prevented, since the rigidity issubstantially uniformly improved along the cutting planes 524 f and 524f in the sheet member 524, and along the cutting planes 525 f and 525 fin the sheet member 525.

The flange member 522 enables easy positioning of the sheet member 524with respect to the sheet member 525. This is because the sheet member524 can be positioned with respect to the sheet member 525 only bymaking the cutting planes 524 f and 524 f of the sheet member 524coincide with the lower end (corner) of the inclined faces of theintermediate portions 525 d and 525 e in the sheet member 525. In theflange member 522 illustrated herein, the length L24 in the extrusiondirection of the sheet member 524 is set equal to the width (frontwidth) W525 of the inner portion 525 a of the sheet member 525 for theconvenience of positioning. In such sheet members 524 and 525, thelength L524 may be set smaller than the width W525. Likewise, the lengthL525 may be set larger than or smaller than the width W524.

A flange member 532 illustrated in FIGS. 46 and 47 comprises two sheetmembers 534 and 535 which are overlaid with each other and have a roundhole 536 at the center thereof, which hole 536 penetrates in a thicknessdirection. With reference to FIG. 46, the sheet member 534 is made of analuminum alloy extrudate having the same cross sectional shape as thesheet member 524 and is formed by cutting the extrudate in a planeinclined to a plane perpendicular to the extrusion direction to apredetermined length. In FIG. 46, the case where an extrudate is cut ina plane perpendicular to the extrusion direction is indicated by avirtual line. Likewise, the sheet member 535 is made of an aluminumalloy extrudate having the same cross sectional shape as the sheetmember 525 and is formed by cutting the extrudate in a plane inclined toa plane perpendicular to the extrusion direction to a predeterminedlength.

The flange member 532 as illustrated in FIG. 47 is formed by overlayingthe sheet member 534 on the sheet member 535 in their inner portions sothat their extrusion directions intersect with each other. Theintersecting angle between the two sheet members 534 and 535 is notsquare (90 degrees), in contrast to the flange member 522. However, theflange member 532 is so configured that the both cutting planes of thesheet member 534 are in parallel with the extrusion direction of thesheet member 535 and that the both cutting planes of the sheet member535 are in parallel with the extrusion direction of the sheet member534, as in the flange member 522. Although not illustrated in detail,the flange member 532 has a similar configuration to that of the flangemember 522 in that the cutting planes of the sheet member 534 arepositioned at a rigid end (at the corner formed with the intermediateportion) of the inner portion in the sheet member 535 and that thecutting planes of the sheet member 535 are positioned at a rigid end (atthe corner formed with the intermediate portion) of the inner portion inthe sheet member 534.

An axial member with flange (not shown) produced by using the flangemember 532 will exhibit similar operation and advantages to the axialmember with flange 521.

A flange member 542 illustrated in FIGS. 48 and 49 comprises two sheetmembers 544 and 545 which are overlaid with each other and each have around hole 546 at the center penetrating in a thickness direction. Thesheet member 544 is made of an aluminum alloy extrudate and is formed bycutting the extrudate in a plane perpendicular to the extrusiondirection to a predetermined length (L544). The sheet member 544 hasbasically the same cross sectional structure as the sheet member 524 andcomprises an inner portion 544 a, outer portions 544 b and 544 c, andintermediate portions 544 d and 544 e. The sheet member 545 is made ofan aluminum alloy extrudate and is formed by cutting the extrudate in aplane perpendicular to the extrusion direction to a predetermined length(L545). The sheet member 545 has basically the same cross sectionalstructure as the sheet member 525 and comprises an inner portion 545 a,outer portions 545 b and 545 c, and intermediate portions 545 d and 545e. With reference to FIGS. 48( a) and 48(b), the sheet member 544 has agroove 547 with a width W547 in the rear face of the inner portion 544a; and the sheet member 545 has a groove 548 with a width W548 in thefront face of the inner portion 545 a.

The length L544 of the sheet member 544 is substantially equal to thewidth W548 of the groove 548, and the length L545 of the sheet member545 is substantially equal to the width W547 of the groove 547.Consequently, the two grooves 547 and 548 will engage with each otherwhen the sheet members 544 and 545 are overlaid other so that theirextrusion directions intersect with each other at the right angle.

The sheet members 544 and 545 in the flange member 542 each have asmaller thickness than that of the other region in a regioncorresponding to the grooves 547 and 548, namely, in a region where thetwo members are overlaid in the inner portions 544 a and 545 a. As aresult of overlaying the two members, however, the region as a whole hasa thickness similar to that of the other regions. The flange members 522and 532 each have, in an overlaying region, a thickness two times largerthan that of a single sheet member not overlaid and have a high rigiditycorresponding to the thickness in the region. When a flange member doesnot need such a high rigidity, it may have a small thickness in a regionwhere the sheet members are overlaid so as to reduce its weight as inthe flange member 542, as long as a necessary rigidity is obtained.

The flange member 542 enables easy positioning between the two sheetmembers 544 and 545, since the sheet members 544 and 545 have thegrooves 547 and 548 in the inner portions 544 a and 545 a.

A flange member 552 illustrated in FIG. 50 comprises two sheet members554 and 555 which are overlaid with each other and each have a roundhole 556 at the center penetrating in a thickness direction. The sheetmember 554 resembles the sheet member 544 in having a groove 557 in therear but differs therefrom in having neither outer portions norintermediate portions and having only a portion corresponding to theinner portion 544 a of the sheet member 544. The sheet member 555 hasthe same configuration as the sheet member 545. More specifically, thesheet member 555 has a groove 558 in the front of an inner portion 555a; the sheet member 554 has a length L554 substantially equal to thewidth W558 of the groove 558; the sheet member 555 has a length L555substantially equal to the width W557 of the groove 557; and the twogrooves 557 and 558 engage with each other.

An axial member with flange (not shown) produced by using the flangemember 552 exhibits similar operation and advantages to those of theaxial member with flange produced by using the flange member 542, exceptfor having only two portions (outer portions 555 b and 555 c) to serveas a mounting face in the front face instead of four portions (fourouter portions).

Connection members according to the present invention will beillustrated in more detail with reference to FIGS. 51 to 64 by takingbumper stays as an example.

A bumper stay 620 shown in FIG. 51 is to be mounted to an inclinedmating face at the end of a bumper reinforcement and comprises a hollowmember 621 and an axial member 622, each of which is made of an aluminumalloy extrudate.

As clearly illustrated in FIG. 52, the hollow member 621 comprises asheet first flange 623, a sheet second flange 624 and pair of ribs 625and 626 connecting these flanges. The first flange 623 has steps, inwhich its center part 627 is positioned to the rear of mounting sections628 to be in contact with the bumper reinforcement. The center part 627has a hole 629 into which the axial member 622 is mounted. Likewise, thesecond flange 624 has steps, in which a center part 631 is positioned tothe rear of a mounting sections 632 to be in contact with a side member.The center part 631 has a hole 633 into which the axial member 622 is tobe mounted. The holes 629 and 633 each have a round shape when viewedfrom a direction perpendicular to the center part 631 and have adiameter substantially equal to the width of the center parts 627 and631. In this connection, the hole 629 has a somewhat elliptic shape whenviewed from a direction perpendicular to the center part 627. The ribs625 and 626 connect the center parts 627 and 631 of the first and secondflanges and the vicinities at corners of ramps 634 and 635 and curveoutward. FIG. 52 illustrates bolt holes 636 for fixing.

With reference to FIGS. 54 and 55, the axial member 22 is placed intothe holes 629 and 633 at both ends, expands as a result ofelectromagnetic forming and comes into intimate contact with the innerperipheries of the holes 629 and 633. In addition, portions of the axialmember 22 protruding frontward from the holes 629 and 633 flare in aradial direction to form flared portions 637 and 638, and a portion ofthe axial member 22 between the first and second flanges 623 and 624expands as a result of electromagnetic forming and protrude outward in aradial direction to form a protrusion 639. The flared portions 637 and638 are in contact with the ramps 634 and 635 partially in acircumferential direction and are in contact with the center parts 627and 631 in the other region. The tips of the axial member 622 arepositioned to the rear of the mounting sections 628 and 632 in the firstand second flanges 623 and 624. The protrusion 639 hits against the ribs625 and 626 and is in intimate contact with them in part of thecircumferential direction near to the ribs 625 and 626 (FIG. 54) andfreely deforms (protrudes) in the other region in accordance withworking force formed during electromagnetic forming. Thus, the axialmember 622 is, at both ends, in intimate contact with the innerperipheries of the first and second flanges 623 and 624 around the holes629 and 633 and is thereby fixed to the first and second flanges 623 and624 of the hollow member 621. The center parts 627 and 631 are pinchedby the flared portion 637 and 638 and the protrusion 639.

A production method of the bumper stay 620 is shown in FIG. 53. An axialmaterial 641 having a circular cross section is inserted, at its bothends, into the holes 629 and 633 in the first and second flanges 623 and624 of the hollow member 621 so that tips of the axial material 641protrude frontward (the virtual line in FIG. 53). The axial material 641is cut at one end in a plane perpendicular to the axial direction and iscut at the other end in a plane inclined with respect to theabove-mentioned plane. The axial material 641 is placed in the holes 629and 633 so that a cutting plane at the one end is in parallel with thesecond flange 624 and a cutting plane at the other end is in parallelwith the first flange 623. Namely, the lengths of regions protrudingfrom the holes 629 and 633 are uniform in a circumferential direction.

The axial material 641 in this state is positioned with respect to thehollow member 621, an electromagnetic forming coil 642 is inserted intothe axial material 641, an electric energy is applied and thuselectromagnetic forming is carried out, and the axial material 641 isallowed to expand in a radial direction. Thus, the above-mentionedbumper stay 620 is produced.

In the bumper stay 620, the axial member 622 is, at its both ends, inintimate contact with the inner peripheries of the holes 629 and 633 andis, in part of the protrusion 639, in intimate contact with the ribs 625and 626; and the protrusion 639 has a varying shape in a circumferentialdirection, namely, a region which has freely deformed protrudes morethan a region which has been in intimate contact with the ribs.Consequently, the axial member 622 is prevented from rotating in theholes 629 and 633 even if a force acts to relatively rotate the axialmember 622 and the hollow member 621. In addition, the first flange 623particularly in the center part 627 having the hole 629 is inclined to aplane perpendicular to the axial direction of the axial member 622. Thisalso prevents the rotation.

FIG. 56 illustrates a bumper stay 644 having another configuration. Thebumper stay 644 has a hollow member 645. The hollow member 645 has thesame configuration as the hollow member 621, except that ribs 648 and649 connecting first and second flanges 646 and 647 are flat. The axialmember 651 has a protrusion 652. The axial member 651 has the sameconfiguration as the axial member 622, except that the protrusion 652 isblocked by and is in intimate contact with the ribs 648 and 649 in partof a circumferential direction near to the ribs 648 and 649 and becomesflat in this region. The other region of the protrusion 652 freelydeforms (protrudes) in accordance with working force as a result of theelectromagnetic forming.

In this configuration, the axial member 651 at the protrusion 652 ismore intensively pressed to and becomes in more secure contact with theribs 648 and 649.

FIGS. 57 and 58 illustrate a bumper stay 653 having yet anotherconfiguration. The bumper stay 653 comprises a hollow member 654 and anaxial member 659. The hollow member 654 has the same configuration asthe hollow member 621, except that ribs 657 and 658 connecting first andsecond flanges 655 and 656 are arranged at both ends of the first andsecond flanges 655 and 656 and are flat. The axial member 659 has thesame configuration as the axial member 622, except that the axial member659 is arranged away from the ribs 657 and 658, and a protrusion 660 ofthe axial member 659 is not in intimate contact with the ribs 657 and658 and freely deforms (protrudes) in its whole circumference inaccordance with working force as a result of electromagnetic forming.

This configuration increases stability under a load, since the distancebetween the ribs 657 and 658 is wide. In contrast, the first and secondflanges 655 and 656 are susceptible to distortion when the axial member659 instantaneously expands upon electromagnetic forming to yield aforce to widen the inner peripheries of holes (holes 629 and 633 of thehollow member 621) in a radial direction. This is because the axialmember 659 is arranged at a wide distance from the ribs 657 and 658. Inthis connection, the hollow member 621 serves to prevent the distortionof the first and second flanges 623 and 624 upon electromagneticforming, since the mounting sections 628 and 632 of the first and secondflanges 623 and 624 are positioned outside the ribs 625 and 626, namely,the ribs 625 and 626 are positioned in the vicinity of the holes 629 and633, and the ribs 625 and 626 serve as a support against the distortion.In addition, the bumper stay 620 is easy to mount to a bumperreinforcement and a side member, since the mounting sections 628 and 632are positioned outside the ribs 625 and 626.

FIGS. 59 and 60 illustrate a bumper stay 661 having anotherconfiguration. The bumper stay 661 comprises a hollow member 662 and anaxial member 669. It has substantially the same configuration as above,except that holes 667 and 668 arranged in center parts 665 and 666 offirst and second flanges 663 and 664 have diameters being not equal tobut smaller than the widths of the center parts 665 and 666, and thatportions of the axial member 669 protruding frontward from the hole 667and 668 and spreading in a radial direction in the form of a flange(flared portions 671 and 672) are not in contact with the center parts665 and 666 in its whole circumference.

This configuration has substantially no disadvantages caused by theflared portions 671 and 672 of the axial member 669 being not in contactwith the center parts 665 and 666 of the first and second flanges 663and 664. In contrast, the configuration yields an advantage inproduction in that such a small electromagnetic forming force as notmake the flared portions 671 and 672 come in contact with the centerparts 665 and 666 will do. This reduces the force to widen the innerperipheries of the holes 667 and 668 in a radial direction, which forceis induced by the expanding axial member 669 upon electromagneticforming and thereby prevents distortion of the first and second flanges663 and 664. The configuration also prolongs the lives of theelectromagnetic forming coil, control devices, and other facilities,since there is not need of applying an excessively high electric energyto the electromagnetic forming coil.

FIG. 61 illustrates a bumper stay 674 having yet another configuration.The bumper stay 674 is also to be mounted to an inclined mating face atthe end of a bumper reinforcement and comprises a hollow member 675 andan axial member 676.

The hollow member 675 comprises two sheet members 677 and 678 each ofwhich is made of an aluminum alloy extrudate (FIGS. 62 and 63) andcomprises a sheet first flange 679, a sheet second flange 680 and pairof ribs 681 and 682 connecting these flanges. The first flange 679 hassteps and comprises a center part 683, a mounting section 684 to be incontact with a bumper reinforcement, and a ramp 685 connecting thecenter part 683 and the mounting section 684. The center part 683 isrecessed with respect to (located to the rear of) the mounting section684. The center part 683 has a hole 686 into which an axial member 676is to be mounted. The second flange 680 has no steps and serves, as awhole, as a mounting section to be in contact with a side member. Thesecond flange 680 has a burring hole 687 substantially in the centerthereof, into which the axial member 676 is to be mounted. The holes 686and 687 each have a circular shape when viewed from a directionperpendicular to the second flange 680. The hole 686 has a somewhatelliptic shape when viewed from a direction perpendicular to the centerpart 683.

With reference to FIG. 62, one member 677 for constituting the hollowmember 675 is a sheet member having steps and comprises outer portions688, the center part 683, and ramps 689 connecting the outer portions688 and the center part 683. The center part 683 is recessed withrespect to the outer portions 688 and has the hole 686. The center part683 also has working holes 690 and working notches 691. The outerportions 688 have bolt holes 692 for mounting the bumper reinforcement.The other member 678 for constituting the hollow member 675 comprisesouter portions 693, ramps 694, and the second flange 680. The secondflange 680 has the burring hole 687 and bolt holes 695 for mounting theside member. The outer portions 693 have bolt holes 696.

When the members 677 and 678 are combined to form the hollow member 675,the outer portions 688 and the outer portions 693 are overlaid with eachother to thereby form the mounting section 684; the ramps 689 areoverlaid with upper ends of the ramps 694 to constitute the ramps 685;and the ramps 694 of the member 678 constitute the rib 681,682. Theworking holes 690 and the working notches 691 are positioned at pointscorresponding to the bolt holes 695 for mounting the side member. Thus,a tool can be inserted to carry out bolting. The bolt holes 692 lie overthe bolt holes 696, and at these points stud bolts 697 are pounded orself piercing and clinching nuts 698 are fixed, as illustrated in FIG.61.

With reference to FIG. 61, the axial member 676 at both ends is insertedinto the holes 686 and 687, expands as a result of electromagneticforming, comes into intimate contact with the inner peripheries of thefirst and second flanges 679 and 680 around the holes 686 and 687. Inaddition, a portion of the axial member 676 being near to the firstflange 679 and protruding frontward from the hole 686 spreads outward ina radial direction in the form of a flange to form a flared portion 699and comes into contact with the center part 683 in its wholecircumference. The end of the axial member 676 near to the second flange680 comes into intimate contact with the inner periphery of the secondflange 680 around the burring hole 687 and spreads outward in a radialdirection along the burring hole 687 to form a flared portion 700.

In addition, a portion of the axial member 676 between the first andsecond flanges 679 and 680 protrudes outward in a radial direction toform a protrusion 701 as a result of expansion by electromagneticforming. Thus, the axial member 676 is in intimate contact with theinner peripheries of the first and second flanges 679 and 680 around theholes 686 and 687 at both ends and is fixed to the first and secondflanges 679 and 680 so that the flared portions 699 and 700, and theprotrusion. 701 pinch the center part 683 of the first flange 679 andthe second flange 680. The first flange 679 has steps, and the flaredportion 700 near to the second flange 680 having no steps does notprotrude frontward from the burring hole 687. Consequently, the tips ofthe axial member 676 are positioned to the rear of the mounting sectionsof the first and second flanges 679 and 680 (the mounting section 684and the second flange 680 itself).

A method for producing the bumper stay 674 by fixing the axial member676 to the hollow member 675 is illustrated in FIG. 64. An axialmaterial 702 is, at both ends, inserted into the hole 686 and theburring hole 687 in the first and second flanges 679 and 680 of thehollow member 675, and a tip of the axial material 702 near to the firstflange 679 is protruded frontward (the virtual line in FIG. 64). Theaxial material 702 is made of an aluminum alloy extrudate having acircular cross section. One end thereof is cut in a plane perpendicularto the axial direction, and the other end is cut along a plane inclinedwith respect to the above-mentioned plane. The axial material 702 isplaced in the holes 686 and 687 so that the cutting plane of the one endis in parallel with the second flange 680, and the cutting plane of theother end is in parallel with the first flange 679, namely, the portionprotruding from the hole 679 has a uniform length in a circumferentialdirection.

The axial material 702 in this state is positioned with respect to thehollow member 675, an electromagnetic forming coil 703 is inserted intothe axial material 702, an electric energy is applied to carry outelectromagnetic forming to thereby expand the axial material 702 in aradial direction. Thus, the above-mentioned bumper stay 674 is produced.

The hollow member 675 in the bumper stay 674 comprises the two sheetmembers 677 and 678. This enables easier carrying out of drilling thanin a monolithic hollow member such as the hollow member 621. Drilling iscarried out so that the resulting hole has an axis perpendicular to theflange both in the first flange and the second flange. In the case of ahollow member, the drilling requires extra time and effort such aspositioning of a jig inside the hollow part. In particular, when thehole 629 in the first flange 623 and the hole 633 in the second flange624 have different axes as in the hollow member 621, the two holescannot be opened in one process. In contrast, the members 677 and 678 ofthe hollow member 675 are sheet-like open section members and are easilydrilled. In addition, such open section members can be easily extrudedand the resulting sheets can be molded by pressing.

Other connection members according to the present invention will beillustrated in detail with reference to FIGS. 65 to 78 by taking bumperstays as an example.

A bumper stay 720 shown in FIG. 65 is to be mounted to an inclinedmating section at the end of a bumper reinforcement and comprise aflange member 721 and an axial member 722 each of which is made of analuminum alloy extrudate.

As is clearly illustrated in FIG. 66, the flange member 721 comprises asheet first flange 723, a sheet second flange 724, and a rib 725. Thefirst flange 723 and the second flange 724 are inclined to each otherand are connected by the rib 725. The first flange 723 has steps andcomprises a center part 726, mounting sections 727 to be in contact witha bumper reinforcement, and ramps 728. The center part 726 is recessedwith respect to the mounting sections 727. The flat center part 726 andthe flat mounting sections 727 are in parallel with each other and areconnected by the ramps 728. The center part 727 has a hole 729 formounting the axial member 722. The second flange 724 also has steps andcomprises a center part 731, mounting sections 732 to be in contact witha bumper reinforcement, and ramps 733. The center part 731 is recessedwith respect to the mounting sections 732. The flat center part 731 andthe flat mounting sections 732 are in parallel with each other and areconnected by the ramps 733. The center part 731 has a hole 734 formounting the axial member 722. The holes 729 and 734 each have acircular shape when viewed from a direction perpendicular to the centerpart 731 and have a diameter equal to the widths of the center parts 726and 731. In this connection, the hole 729 has a somewhat elliptic shapewhen viewed from a direction perpendicular to the center part 726. Therib 725 connects narrower ends of the first and second flanges 723 and724 and is perpendicular to the center part 731 of the second flange724. FIG. 66 also illustrates fixing bolt holes 736.

With reference to FIGS. 68 and 69, the axial member 722 is, at bothends, inserted into the holes 729 and 734, expands as a result ofelectromagnetic forming to come into intimate contact with the innerperipheries of the first and second flanges 723 and 724 around the holes729 and 734. In addition, a portion of the axial member 722 protrudingfrontward from the holes 729 and 734 spreads in the form of a flange ina radial direction to form flared portions 737 and 738, and a portion ofthe axial member 722 between the first and second flanges 723 and 724expands as a result of electromagnetic forming and thereby protrudes ina radial direction to form a protrusion 739. The flared portions 737 and738 are, in part in a circumferential direction, in contact with theramps 728 and 733 and are in contact with the center parts 726 and 731in the other region. The tips of the axial member 722 are positioned tothe rear (inside) of the mounting sections 727 and 732 of the first andsecond flanges 723 and 724. The protrusion 739 freely deforms(protrudes) in accordance with working force as a result ofelectromagnetic forming. Thus, the axial member 722 is in intimatecontact with the inner peripheries of the first and second flanges 723and 724 around the holes 729 and 734 at both ends and is fixed to thefirst and second flanges 723 and 724 of the flange member 721, in whichthe flared portions 737 and 738, and the protrusion 739 pinch the centerparts 726 and 731.

A production method of the bumper stay 720 is illustrated in FIG. 67.Initially, an axial material 741 having a circular cross section isinserted into the holes 729 and 734 in the first and second flanges 723and 724 of the flange member 721 at both ends so that the tips of theaxial material 741 protrude frontward from the holes (the virtual linein FIG. 67). The axial material 741 is cut at one end in a planeperpendicular to the axial direction and is cut at the other end in aplane inclined with respect to the above-mentioned plane. The axialmaterial 741 is placed in the holes 729 and 734 so that a cutting planeat one end is in parallel with the center part 731 of the second flange724, and a cutting plane at the other end is in parallel with the centerpart 726 of the first flange 723. Namely, the axial material 741protrudes from the holes 729 and 734 with uniform lengths in acircumferential direction.

The axial material 741 in this state is positioned with respect to theflange member 721, and an electromagnetic forming coil 742 is insertedinto the axial material 741. A jig 743 for preventing deformation isthen inserted into the open side of the flange member 721, an electricenergy is applied and electromagnetic forming is carried out to therebyexpand the axial material 741 in a radial direction. Thus, theabove-mentioned bumper stay 720 is produced.

In the resulting bumper stay 720, the center parts 726 and 731 of thefirst and second flanges 723 and 724 are recessed from the mountingsections 727 and 732, and thereby the tips (flared portions 737 and 738)of the axial member 722 can be positioned to the rear (inside) of thefront faces of the mounting sections 727 and 732, even though theyprotrude frontward from the holes 729 and 734. Consequently, the tips ofthe axial member 722 protruding frontward from the holes 729 and 734 donot obstruct the mounting of the mounting sections 727 and 732 to othermembers (the bumper reinforcement and the side member).

In the bumper stay 720, the rib 725 of the flange member 721 serves tosupport a load applied upon collision, together with the axial member722. The rib 725 is resistant to buckling (collapse) upon collisionbecause of the reinforcement by the axial member 722 and thereby servesto support the load satisfactorily. The bumper stay 720 also highlyabsorbs energy by the action of accordion-fold deformation of the axialmember 722.

The bumper stay 720 uses the flange member 721 comprising the first andsecond flanges 723 and 724 connected by the rib 725. This uniquelydetermines the positional relationship between the first and secondflanges 723 and 724 and thereby enables easy positioning between theaxial member 722 and the first and second flanges 723 and 724 uponelectromagnetic forming. In addition, the jig 743 for preventingdeformation can be easily inserted into the flange member uponelectromagnetic forming, since the rib 725 connects the narrower ends ofthe first and second flanges 723 and 724.

In the bumper stay 720, the axial member 722 is in intimate contact withthe inner peripheries of the first and second flanges 723 and 724 aroundthe holes 729 and 734 at both ends; the flared portions 737 and 738 arein contact with the ramps 728 and 733 partly in a circumferentialdirection; and the first flange 723 particularly in the center part 726having the hole 729 is inclined with respect to a plane perpendicular tothe axial direction of the axial member 722. These prevent the axialmember 722 from rotating in the holes 729 and 734 even if a force actsto relatively rotate the axial member 722 and the flange member 721 (theflanges 723 and 724).

FIGS. 70 and 71 illustrate a bumper stay 750 having anotherconfiguration. The bumper stay 750 has substantially the sameconfiguration as the bumper stay 720, except that a rib 755 forconnecting first and second flanges 753 and 754 of a flange member 751connects the vicinities at the corners of center parts 756 and 757 andramps 758 and 759; that holes 761 and 762 arranged in the center parts756 and 757 of the first and second flanges 753 and 754 have diametersnot equal to but smaller than the widths of the center parts 756 and757; and that portions of the axial member 752 protruding frontward fromthe holes 761 and 762 and spreading as a flange (flared portion 763 and764) are not in contact with the center parts 756 and 757 in its wholecircumference.

The bumper stay 750 is resistant to distortion of the first and secondflanges 756 and 757 as being supported by the rib 755 when the axialmember 752 instantaneously expands to yield force to widen the innerperipheries of the holes 761 and 762 outward in a radial direction uponelectromagnetic forming. This is because the rib 755 of the flangemember 751 is positioned in the vicinity of the holes 761 and 762. Inaddition, the bumper stay 750 can be easily mounted to a bumperreinforcement and a side member, since the mounting sections 765 and 766of the flange member 751 is positioned outside the rib 755.

The bumper stay 750 has substantially no disadvantages caused by theflared portions 763 and 764 of the axial member 752 being not in contactwith the center parts 756 and 757 of the first and second flanges 752and 753. In contrast, this configuration yields an advantage inproduction in that such a low electromagnetic forming force as not makethe flared portions 763 and 764 come in contact with the center parts756 and 757 will do. This reduces the force to widen the innerperipheries of the holes 761 and 762 in a radial direction, which forceis induced by the expanding axial member 752 upon electromagneticforming. Thus distortion of the first and second flanges 752 and 753 isprevented. The configuration also prolongs the lives of theelectromagnetic forming coil, control devices, and other facilities,since there is no need of applying an excessively high electric energyto the electromagnetic forming coil.

FIG. 72 illustrates a bumper stay 770 having yet another configuration.The bumper stay 770 is also to be mounted to an inclined mating sectionat the end of a bumper reinforcement and comprises a flange member 771and an axial member 772.

The flange member 771 includes a combination of two sheet members 773and 774 (FIGS. 73 and 74) each of which is made of an aluminum alloyextrudate and comprises a sheet first flange 775, a sheet second flange776, and a rib 777 connecting these flanges. The first flange 775 hassteps and includes a center part 778 and mounting sections 779 to be incontact with a bumper reinforcement. The center part 778 is recessedfrom the mounting sections 779. The flat center part 778 and the flatmounting sections 779 outside thereof are in parallel with each otherand are connected by ramps 781. The center part 778 has a hole 782 formounting the axial member 772. The second flange 776 has no steps andserves, as a whole, a mounting section to be in contact with a sidemember. The second flange 776 has a burring hole 783 for mounting theaxial member 772 substantially in the center thereof and has a holeflange 780 around the burring hole 783. The holes 782 and 783 each havea circular shape when viewed from a direction perpendicular to thesecond flange 776. The hole 782 has a somewhat elliptic shape whenviewed from a direction perpendicular to the center part 778.

With reference to FIG. 73, one member 773 for constituting the flangemember 771 is a sheet member having steps and comprises outer portions784, ramps 785, and the center part 778. The center part 778 is recessedwith respect to the outer portions 784 and is connected thereto via theramps 785. The center part 778 has the hole 782 and also has workingholes 786 and working notches 787. As illustrated in FIG. 74, the outerportions 784 have bolt holes 788 for mounting a bumper reinforcement.The other member 774 for constituting the flange member 772 comprises anouter portion 789 at one end, a ramp 791 and the second flange 776. Thesecond flange 776 has the burring hole 783 and also has bolt holes 792for mounting a side member, and the outer portion 789 has bolt holes793.

When the members 773 and 774 are combined to constitute the flangemember 771, the outer portion 784 and the outer portion. 789 areoverlaid with each other to constitute the mounting section 779 (theleft mounting section 779 in FIG. 72); the ramp 785 and the upper end ofthe riser or ramp 791 are overlaid with each other to constitute theramp 781 (the left ramp 781 in FIG. 72); and the ramp 791 of the member774 constitutes the rib 777. The working holes 786 and the workingnotches 787 are positioned at points corresponding to the bolt holes 792for mounting the side member. Thus, a tool can be easily inserted tocarry out bolting. The bolt holes 788 lie over the bolt holes 793, andat these points stud bolts 794 are pounded as illustrated in FIG. 72.

With reference to FIG. 72, the axial member 772 is inserted, at bothends, into the holes 782 and 783, expands as a result of electromagneticforming and comes into intimate contact with the inner peripheries ofthe first and second flanges 775 and 776 around the holes 782 and 783. Aportion of the axial member 772 near to the first flange 775 andprotruding frontward from the hole 782 spreads in a radial direction inthe form of a flange to form a flared portion 795 and comes into contactwith the center part 778 in its whole circumference. The end of theaxial member 772 near to the second flange 776 is in intimate contactwith the inner periphery of the burring hole 783, spreads outward in aradial direction along the burring hole 783 to form a flared portion796. In addition, a portion of the axial member 772 between the firstand second flanges 775 and 776 protrudes outward in a radial directionas a result of expansion by electromagnetic forming, to form aprotrusion 797. The axial member 772 is, at both ends, in intimatecontact with the inner peripheries and is fixed to the first and secondflanges 775 and 776 around the holes 782 and 783, in which the flaredportions 795 and 796, and the protrusion 797 pinch the center part 778of the first flange 775 and the second flange 776. The first flange 775has steps, and the flared portion 796 near to the second flange 776having no steps does not protrude frontward from the burring hole 783.Consequently, the tips of the axial member 772 are positioned to therear (inside) of the mounting sections of the first and second flanges775 and 776 (the mounting section 779 and the second flange 776 itself).

A method for fixing the axial member 772 to the flange member 771 andthereby producing the bumper stay 770 is shown in FIG. 75. Initially, anaxial material 790 is inserted into the hole 782 and the burring hole783 formed in the first and second flanges 775 and 776 of the flangemember 771, and a tip thereof near to the first flange 775 is protrudedfrontward from the hole (the virtual line in FIG. 75). The axialmaterial 790 is made of an aluminum alloy extrudate having a circularcross section, is cut at one end in a plane perpendicular to the axialdirection, and is cut at the other end in a plane inclined with respectto the above-mentioned plane. The axial material 790 is placed in theholes 782 and 783 so that a cutting plane at the one end is in parallelwith the second flange 776, and a cutting plane at the other end is inparallel with the center part 778 of the first flange 775, namely, theportion protruding from the hole 782 has a uniform length in acircumferential direction.

The axial material 790 in this state is positioned with respect to theflange member 771, an electromagnetic forming coil 798 is inserted intothe axial material 790, and a jig 799 for preventing deformation isinserted into the open side of the flange member 771. Then, an electricenergy is applied and electromagnetic forming is carried out to therebyexpand the axial material 790 in a radial direction. Thus, theabove-mentioned bumper stay 770 is produced.

The flange member 771 in the bumper stay 770 comprises two sheet members773 and 774. This enables easier carrying out of drilling than in amonolithic flange member such as the flange member 721. Drilling iscarried out so that the resulting hole has an axis perpendicular to theflange, both in the first flange and the second flange. In the case of amonolithic flange member, the drilling requires extra time and effortsuch as positioning of a jig between the two flanges. In particular,when the hole 729 of the first flange 723 and the hole 734 of the secondflange 724 have different axes as in the hollow member 721, the twoholes cannot be opened in one process. In contrast, the members 773 and774 in the flange member 771 are sheet-like open section members and areeasily drilled. In addition, such open section members can be easilyextruded and the resulting sheets can be molded by pressing.

FIG. 76 illustrates a bumper stay 800 having another configuration. Thebumper stay 800 is also to be mounted to an inclined mating section atthe end of a bumper reinforcement and comprises a flange member 801 andan axial member 802. The flange member 801 comprises two members 803 and804, as in the flange member 771. The bumper stay 800 differs from thebumper stay 770 in that holes arranged in first and second flanges 805and 806 are burring holes 807 and 808 which have been burred from thefront. Hole flanges 809 and 810 are arranged around the burring holes807 and 808, respectively.

The axial member 802 is at both ends inserted into the burring holes 807and 808, expands as a result of electromagnetic forming and comes intointimate contact with the inner peripheries of the burring holes 807 and808 and spreads in a radial direction along the burring holes 807 and808 to form flared portions 811 and 812. In addition, a portion of theaxial member 802 between the first and second flanges 805 and 806protrudes outward in a radial direction as a result of expansion byelectromagnetic forming, to form a protrusion 813. A tip of the axialmember 802 near to the first flange 805 protrudes frontward (outward)from the burring hole 807 but is recessed (positioned inside) withrespect to the mounting section 815. This is because the first flange805 has steps, and the center part 814 bearing the burring hole 807 isrecessed with respect to the mounting section 815 to be in contact witha bumper reinforcement. A tip of the axial member 802 near to the secondflange 804 having no steps does not protrude frontward (outward) fromthe burring hole 806, as in the flared portion 796 in the bumper stay770.

FIG. 77( b) illustrates a member 816 as a modification of the member 803in the bumper stay 800. The member 816 has a burring hole in a centerpart 817, and a hole flange 818 around the burring hole. The hole flange818 has plural vertical slits 819. With reference to FIG. 77( a), thehole flange having the slits 819 is formed by forming slits 821 in aradial direction in the periphery of a pilot hole 820 in a center part817 of the member 816 and burring the pilot hole 820. The presence ofthe slits 819 enables more secure fixing of the axial member 802 and theburring hole and more secure prevention of rotation of the axial member802 with respect to the burring hole, since the molded axial member 802(FIG. 76) protrudes and fits into the slits 819 when an axial materialis inserted into the burring hole and is expanded by electromagneticforming.

FIG. 78 illustrates a member 823 as a modification of the member 803 inthe bumper stay 800, and a method for processing a burring hole of themember 823. In the member 803, burring is carried out in a directionperpendicular to the plane of the center part 778, and the axis of thehole flange 809 is perpendicular to the plane of the center part 778. Incontrast, the member 823 after forming a pilot hole is placed in a die824 as being inclined, and is pressed by a sheet presser 825, and apunch 826 is pressed into the pilot hole, as illustrated in FIG. 78. Theburring is therefore carried out in an oblique direction with respect tothe plane of the center part 827, and the resulting hole flange 828formed around the burring hole has a center axis inclined with respectto the plane of the center part 827. The inclination is set so that itagrees with the inclination of axial member (and the axial material)with respect to the first flange (center part 826), namely, so that theaxis of the hole flange 827 is in parallel with the axis of the axialmember (and the axial material). The axes of the hole flange 828 and theaxial material point the same direction, and thereby the axial materialcan be precisely fit into the burring hole upon electromagnetic forming.

The present invention has been specifically illustrated mainly by takingbumper stays as an example. The axial members with flange according tothe present invention, however, can also be generally applied to otheraxial members with flange to be mounted to a counter member, such as areinforcement for instrument panel, a cross member, a channel side-rail,a tower bar, an attached pipe for instrument panel (a pipe one end ofwhich is mounted to a instrument panel reinforcement and serves tosupport the instrument panel or a duct), a pillar, a seat frame, anintake manifold, a muffler, a propeller axial section and a steeringcolumn of motor vehicles such as passenger cars and trucks, a swingingarm for two-wheel vehicles including bicycles, as well as a seat framefor aircraft, a frame for chair, and joints for various applications.

Whether a flange member is joined to both ends or to one end of an axialmember may be arbitrarily selected according to the usage of a targettubular member with flange.

1. An axial member with flange, comprising: a flange member having amounting face to be in contact with a mating face of another member; andan axial member being made of a tubular aluminum alloy material andhaving an end joined to the flange member, wherein the flange member hasa hole, and the axial member is placed in the hole, wherein the axialmember has a flared portion at an end thereof, the flared portionspreading in a radial direction as a result of electromagnetic formingand being in intimate contact with the flange member, wherein the axialmember has a protrusion formed by electromagnetic forming, and theflange member on the periphery of the hole is held between the flaredportion and the protrusion, and wherein the flange member has athick-walled portion in a region where the flared portion is in intimatecontact with the flange member.
 2. The axial member with flangeaccording to claim 1, wherein the flange member has a thick-walledportion in a region around the hole in part or all of thecircumferential direction and has a smaller thickness than that of thethick-walled portion in a region outside the thick-walled portion. 3.The axial member with flange according to claim 1, wherein the flangemember is made of an aluminum alloy extrudate and has a thick-walledportion in the vicinity of the hole when viewed in a cross sectionperpendicular to the extrusion direction, the rear face of the flaredportion is in intimate contact with the thick-walled portion, and theflange member has a smaller thickness than that of the thick-walledportion in a region outside the thick-walled portion.
 4. The axialmember with flange according to claim 1, wherein the flange member ismade of an aluminum alloy extrudate and comprises a thick center partand thin regions on both sides of the center part when viewed in a crosssection perpendicular to the extrusion direction, the hole is arrangedin the center part, and the rear face of the flared portion is incontact with the center part.
 5. A method for producing a tubular memberwith flange, comprising the steps of inserting an axial membercomprising a tubular aluminum alloy material into a hole of a sheetflange member; protruding the tip of the axial member outward in anaxial direction from the hole to a predetermined length; and expandingthe axial member by electromagnetic forming, Wherein, as a result of theexpansion, the axial member is brought into intimate contact with theinner rim of the hole and the protrusion of the axial member protrudingfrom the hole is spread and is brought into intimate contact with theflange member, and wherein the axial member inside of the flange memberin an axial direction is protruded outward in a radial direction so asto join the flange member to an end of the axial member.